Step-by-step explanation:

The Answer is C, my good friend.
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
The hypotenuse is the square root of 58.
a^2+b^2=c^2
7^2+3^2=c^2
49+9=c^2
58=c^2
c= square root of 58