a) To solve for x, we can cross multiply:
5 * x = 4 * 15
5x = 60
Divide both sides by 5:
x = 12

b) To solve for x, we can cross multiply:
9 * x = -4 * 27
9x = -108
Divide both sides by 9:
x = -12

c) To solve for x, we can cross multiply:
x * -27 = 6 * -18
-27x = -108
Divide both sides by -27 (remember to flip the inequality sign since we're dividing by a negative number):
x = 4

d) To solve for x, we can cross multiply:
45 * x = 6 * -27
45x = -162
Divide both sides by 45:
x = -3.6