I know how to do it I think, look at photo

Use the pythagorean theorem: a^2+b^2=c^2. a=x, b=24 and c=26. no plug those numbers in and you should have x^2+576=676. now in order so find x, isolate the variable. 676-576=100. x^2=100. square root of 100 is 10 so x=10