The way this is traditional done is to find the hypotenuse of 5 and 10 inches and use this result with the height. If that does not work, then other combinations can be used.
Hypotenuse (10 and 5 )
Formula
c^2 = a^2 + b^2
Givens
a = 10
b = 5
Solution
c^2 = 10^2 + 5^2 Expand
c^2 = 100 + 25 Add
c^2 = 125
Now use the Pythagorean Theorem a second time.
z^2 = x^2 + y^2
x^2 = 125
y^2 = 3^2
z^2 = 125 + 9
z^2 = 134
This is not large enough. A ruler is 12 inches long which would mean that z^2 should come to 144. I don't think any other combination is going to do much better.
In fact looking at it more closely all combinations will give z^2 = 134.
