Algebra

Crikey, that's an awful lot of pens. What in earth was James doing with them all?!

Please give me a step by step solution to the question. In advance, Thanks.

No. This isn't how TSR works - it's not a free homework service, or ChatGPT.

You need to post up what you have so far, and then people will be happy to help you refine your answer.

The pens are sold only in packs, so it's probably best to label pack of blue=x , pack of green=y.
You know a pack of blue costs £5, so the total amount will be 5x. Same process for green. You also know what the difference between the cost of both
You know the total amount of blue pens will be 4x, again do the same for green. You know you will have an equal number of pens of each colour.
You can set up 2 equations and then solve for the number of blue pens he's bought.

am sorry, i dont follow

#5 looks promising but a bit complex? You could try and verify 175 and see if the price difference is 84.

But Id be tempted to work out the difference in price for 1 pen (green - blue) and simply divide 84 by that.

Like no cap, am really confused

About what? Working out the price difference (green - blue) for 1 pen, or divding 84 by that or ...?

am sorry, i dont follow

what is green minus blue

Which part don't you follow?

price of 1 green pen - price of 1 blue pen

i got the right answer, but dont know why?

Post what you thought / which part youre confused about.

basically done as u suggested:
(8/5 - 5/4)x = 84
(32/20 - 25/20) x = 84
20*(7/20)x = 84*20
7x/7 = 1680/7
x = 240
came forth with the right answer, but dont know why and where the x came from, just added the x in for optic

When you formulate the original equation, try and write down clearly what each of the parts represent so
(8/5 - 5/4) ....
x ...
84 ...
As its algebra, it should balance.

You know a pack of blue costs £5, so the total amount will be 5x. Same process for green. You also know what the difference between the cost of both
You know the total amount of blue pens will be 4x, again do the same for green. You know you will have an equal number of pens of each colour.
You can set up 2 equations and then solve for the number of blue pens he's bought.