Question 218859
Hint: use the Pythagorean theorem {{{a^2+b^2=c^2}}}. In this case, {{{a=30}}} and {{{b=40}}} and we'll let {{{c=x}}}. So plugging this in gets us {{{(30)^2+(40)^2=x^2}}}. From here, just solve for 'x' to find the length of 'c'. Let me know if this is enough to get you started.