Question 510937
Matthew is 3 times as old as Jenny.
m = 3j
 In 7 years he will be twice as old as she will be then.
m + 7 = 2(j+7)
m + 7 = 2j + 14
m = 2j + 14 - 7
m = 2j + 7
Replace m with 3j
3j = 2j + 7
3j - 2j = 7
j = 7 yrs
then obviously
m = 21 yrs