Help my mind went blank and idr how to solve it

What properties allow transformation to be used as a problem solving tool

William invested $5000 in an account that earns 3.8% interest, compounded annually. the formula for compound interest is a(t) = p(1 + i)t. how much did william have in the account after 6 years? (apex)

3x + 4y = 5 x- 3y = -7 solve by substitution