one interior angle = 30° <==== this one is given
second interior angle = 180 - 40 = 140° <=== interior angle + exterior angle = 180
third interior angle = 180 - 30 - 140 = 10° <=== angles in a triangle = 180
The sum of two numbers:
x + y = 108
The difference of the same two numbers:
x - y = 78
We can use substitution to figure out x and y:
x - y = 78 can be changed to x = 78 + y
We can plug this into the first equation:
78 + y + y = 108
78 + 2y = 108
2y = 30
y = 15
Now solve for x using any of the two equations. I'll use the first equation since it's easier:
x + 15 = 108
x = 93
