Step-by-step explanation:
a = age of Alex
l = age of Lucy
m = age of Megan
a + l + m = 126
l = 3a
l = m + 7
=>
a = l/3
m = l - 7
we are using that in the first equation :
l/3 + l + l - 7 = 126
l + 3l + 3l - 21 = 378
7l = 357
l = 357/7 = 51
a = l/3 = 51/3 = 17
m = l - 7 = 51 - 7 = 44
the ratio of the age of Lucy to Alex to Megan is
51 : 17 : 44
