To convert temperature from C to F we will use the formula (that you have also given).
[tex]f\text{ = }\frac{9C}{5}+32[/tex]here C = 40, so we have to plug it in the formula, and we will get the answer.
[tex]f\text{ = }\frac{9(40)}{5}+32=104[/tex]There you have it, that is the answer!
