So you're using the Pythagorean theorem which is a^2 + b^2 = c^2... so if you dont have b you can manipulate the equation. That equation is c^2 - a^2= b^2, so you square 47 which is 2209 and then square 13 which is 169... you do 2209-169 and that equals 2040, then you do the square root of that which is 45.166359 that can be simplified to 45 or two decimal points 45.167. Hope that Helped! :)