A Level Maths - Mechanics Q. Please could you kindly help me out with this Q?

A rough plane is inclined to the horizontal at an angle A, where tanA=3/4.
A brick P of mass m is placed on the plane.
The coefficient of friction between P and the plane is Y.
Brick P is in equilibrium and on the point of sliding down the plane.
Brick P is modelled as a particle.
Using the model,
a) find, in terms of m and g, the magnitude of the normal reaction of the plane on brick P
b) Show that Y=3/4

Have you sketched the problem, formed the force equilibrium equations, ...?

Yes this is the answer, but I'm unsure of how to get to that answer
(In the question I used 'Y' instead of 'µ')
(a) Resolve perpendicular to the plane
R =mgcosA = 4/5mg
(b) Resolve parallel to the plane or horizontally or vertically
F mg = sinA or RsinA= FcosA
Use F = µR and solve for µ
µ = 3/4

Did you draw the diagram / what are you unsure about?
Rather than posting someone elses solution, why not post your own working?

That was the markscheme answer. I don't know how to get 3/4 for µ, I get as far as mgsinA/(4/5)mg

What is sin(A)? Im presuming you;ve found cos(A) = 4/5 so its similar.
You know tan(A)=3/4, so ...

Sorry I'm not too sure what you mean

You have a right angled triangle and
tan(A) = 3/4
What is the opposite and adjacent lengths and hence work out the hypotenuse? So then work out cos(A) and sin(A).

I see, but I think you have to use an alternative method for A-Level maths because going via that method doesn't follow through what the markscheme looks for to award marks

You have a right angled triangle and
tan(A) = 3/4
What is the opposite and adjacent lengths and hence work out the hypotenuse? So then work out cos(A) and sin(A).

So I got cosA=4/5 and sinA=3/5, how do you proceed from here to work out µ?