The statement "P is partly constant and varies partly as Q" means P consists of a constant term plus a term directly proportional to Q. Thus, the relationship is: P = a + bQ, where a is the constant part and b is the constant of proportionality. Given: P = 32 when Q = 16 → a + 16b = 32 P = 20 when Q = 12 → a + 12b = 20 Subtract the second equation from the first: (a + 16b) - (a + 12b) = 32 - 20 4b = 12 b = 3 Substitute b = 3 into the second equation: a + 12(3) = 20 a + 36 = 20 a = -16 Thus, P = -16 + 3Q When Q = 28: P = -16 + 3(28) = -16 + 84 = 68