math
posted by jaime .
Roberto and Luisa Barron Lopez each work full time jobs, and Luisa's mother, Carmena, collects a monthly pension of $628. Between the three of them, their total household income is $4238 each month. If Luisa earns $1772, how much does Roberto earn each month?

first, between involves two
among involves more than teo
l = 1772
c = 628
r + 1772 + 628 = 4238
r = 1838