Maths question help please

Hi, please could I have help on part c? How do I workout what the constant A is?
Question: https://ibb.co/5Wq55Lc1
Thanks!

Given that the container is initially empty ...

On your second line of working (red) you have on the left denominator
300*()
rather than
300/()
so the () should be on the numerator.
Note youd expect k to be positive, so -ln(2/3) is the same as ln(3/2) which is neater, as the ms uses.

THANK YOUU sorry I didn’t see it but I’ve tried it again and it works now!

In hindsight, rather than thinking about dividing by 300/(), it would be simpler/less error prone to multiply through the equation by () and divide by 300. Obv the same, but avoids the division by a fraction "problem".