Find value of x, please help

Which expression is equivalent to the expression shown?

At the beginning of year 1, carlos invests $600 at an annual compound interest rate of 4%. he makes no deposits to or withdrawals from the account. which explicit formula can be used to find the account's balance at the beginning of year 5? what is, the balance?

If f(x) = 4x - 3 and g(x) = x + 4, find (f - g) (x)