This is a Pythagorean Theorem problem. 3^2 + 7^2 = 58. C^2 = 58. C = 7.6157 (exact)
There is no exact answer for this. The closest we can get to 58 is 7.6157, which would leave us at 57.9988. So the approximate value is 7.6, but if you need the closest answer, it’s 7.6157.
