Let x = borrowed amount. Let 0.10x = amount of interest (in dollars) William must pay at loan maturity. At maturity, he must pay back the borrowed amt (x) plus the interest on the borrowed amount (0.10x). So, at maturity, he must pay back x + 0.10x, but (according to the problem statement) this equals 30,640. So, we must solve the following equation: 30640 = x + 0.10x, but the right hand side can be factored into 1.10x, so now we need to solve the equation 30640 = 1.10x. Divide both sides of the equation by 1.10, getting x = 27854.55. You can check this by applying the information you are given in the problem statement.