Pythagoren theorem is a^2 + b^2 = c^2
In this case 7^2 + 7^2 =c^2
49 + 49 = 98^2
But you dont want the second number squared so you find the square root if it. In this case square root 98 = 9.899494937
Since it say round to the nearest tenth however it will look more like this 9.9
Good Luck
