System of equations modeling the given conditions:
x + y = 94
x - y = 36
Solving:
In order to use substitution, you have to isolate one of the variables in either of the equations
Using the second equation and isolating the variable x:
x - y = 36
x = 36 + y
then you can substitute x back into the first equation
36 + y + y = 94
36 + 2y = 94
2y = 58
y = 29
and then substitute 29 for y into either one of the equations
x + 29 = 94
x = 65
