c=10.6
Pythageron theorem is
a^2+b^2=c^2
a and b are the legs of the triangle, in this case 8 and 7. The c is the hypotenuse, in this the unknown.
Substitute 8 and 7 in for a and b.
8^2+7^2=c^2
64+49=c^2
113=c^2
Take the square root of both sides
c=10.6301458
Rounded to the nearest tenth
c=10.6
Hope this helps! :)