Answer: 10.25
Step-by-step explanation: use pythagorean theorem; a^2 + b^2 = c^2. 8 would be a, 13 is c, but since you don't have b you leave it as a variable. when you substitute it in you get (8)^2 + b^2 = (13)^2 which is 64 + b^2 = 169. you subtract 64 from both sides and get b^2 = 105. take the square root of both sides to get b = 10.246950766 and round it to 10.25