You can use the pythagorean theorem.
[tex] a^{2} + b^{2} = c^{2}[/tex]
Now lets write out what we know.
Shorter leg = x
Longer Leg = x + 7
Hypotenuse = x - 7
[tex] a^{2} + b^{2} = c^{2}[/tex]
Now solve for x
[tex] x^{2} + (x+7)^{2} = (2x-7)^{2}[/tex]
x = 28
Since you know x = 28, which is the shorter leg, you can solve for the rest by just plugging in 28 where x is located. For instance, longer let is x + 7 so
28 + 7 = 35