Question

Gabrielle is 15 years younger than Mikhail. The sum of their ages is 75 . What is Mikhails age?

Answer 1

Let's use variables and make an equation.
let gabrielle be g, and mikhail be m.
M + G = 75
M = G + 15

Answer 2

Let x = Mikhail's age
x-15 = Gabrielle's age
Add them up and get 75

Answer 3

Using the system,
G = M - 15
as well.
you want M's age. so..
M + M - 15 = 75
2m = 90
m = 45