How do you solve an algebra question with a variable but you also have to find out the initial amount

Question

a person bought a t shirt for $x and spent $(2x+10) on a pair of jeans. After the purchase he is left with $(90-3x). find the initial amount and represent it in an expression showing the total spent

Answer 1

Let A = initial amount.

Then, A - x - (2x + 10) = 90 - 3x.

So, A = 100

Answer 2

x+(2x+10)=p-(90-3x)

3x+10 =p-90+3x

100=p