Question 393882
3M = B
M + 20 = B - 20

This can be simplified to

3M - B = 0
-M + B = 40

+B and -B cancel each other out 

2M = 40
M = 20

once you have M just plug it in to the original equation

3(20) = B
B = 60 

Bettina is 60 and Melvina is 20