The triangle is clearly a right triangle because in AMK, m<M = 90 - so M is definitely 90* making it the base of your right triangle. If AM = 5, MK = 7, they both correlate to the base of your triangle of 90*. Using the pythagorean theorem, 7^2 + 5^2 = 49 + 25 = 74. You then find the square root of 74 which is approximately 8.6.
Answer === 8.6