Question

F(5)= 3.14r^{2} pls help

Answer 1

If you have
.. F(r) = πr^2
and you want to evaluate it for r=5, you put 5 in place of every instance of r, then do the arithmetic.
.. F(5) = π*5^2
.. F(5) = 3.14*25 = 78.5