a)
P = 9 * 10 = 90
P = 5 * 10 = 50
P = 7 * 12 = 84
b)
P = 6 * 4 = 24
P = 5 * 3 : 2 = 15 : 2 = 7,5
P = 5 * 4,8 = 24
c)
P = 8 * 10 : 2 = 80 : 2 = 40
P = 5 * 10 : 2 = 50 : 2 = 25
P = 3 * 4 : 2 = 12 : 2 = 6
d)
P = (1 + 5) * 4 : 2 = 6 * 4 : 2 = 24 : 2 = 12
P = (2 + 6) * 3 : 2 = 8 * 3 : 2 = 24 : 2 = 12
P = (19 + 5) * 5 : 2 = 24 * 5 : 2 = 120 : 2 = 60