the sum of two numbers is 42. three times the first number is the same as four times the other number. find the number.

1) x+y=42
2) 3x=4y 
so...
x=42-y
3x=3(42-y)=4y
3*42-3y=4y 
7y=3*42
y=3*42/7
y=18 
x=42-18
x=24