In the words that your describing it, I supposed we are talking about the pythagorean theorem
What is the formula for the theorem?
a^2+b^2= C^2
A being the height
B being the Bottom
C being the slant or hypotenuse
How to Solve?
Well supposed 9 is a and 6 is b
+
=

9 squared is 81 and 6 squared is 36
81+36= 117
So, 117=

Which means
is the answer or 10.8
Hope this helped!