Answer:
A. 15
Step-by-step explanation:
10 : 9 : 8
Mark: 10x
Tim: 9x
Jane: 8x
(10x - 5) + (9x - 5) + (8x - 5) = 39
10x - 5 + 9x - 5 + 8x - 5 = 39
27x - 5 - 5 - 5 = 39
27x - 15 = 39
27x - 15 + 15 = 39 + 15
27x = 54
27x ÷ 27 = 54 ÷ 27
x = 2
Mark: 10x - 5
10x - 5
10(2) - 5
20 - 5
15