Question

After 15 years Mary's age will be four times of her present age then represent the mary's present age in a linear equation

Answer 1

let y be the present age of the Mary
after 15 years ,
y+15=4y
3y=15
y=5 year

Answer 2

let x be the age of mary after 15 years
x+15=4x
15 = 4x-x
3x=15
x=5....