Answer:
51 and 39
Explanation:
Let's make this into an equation
a + b = 90
and
a - b = 12
Let's merge them
a + b + a - b = 90 + 12
Focus on a for now
2a = 102
a = 51
Now that we have the value of a, we substitute a in any of the 2 equations
51 + b = 90
Subtract 51 from both sides to isolate b
b = 39
We can prove this by adding and subtracting both numbers
51 + 39 = 90
51 - 39 = 12