Beta is a closed economy. The levels of national saving (S) and investment (1) are determined by the following equations: S = 5 + 0.5r I = 10 - 0.5 r Q7 Which of the following is true for Beta in equilibrium? (a) r = 5 and | = 7.5 (b) r = 5 and S = 7.5 (c) S = 5 and I = 5 (d) both (a) and (b) (e) none of the above