Are you too lazy to find an online resource or something? We won't spoonfeed you everything.
... that's so easy, just go plug it into a calculator and you'll get the answer.
To convert a fraction into a percent we need to first simply the fraction then... turn it into a decimal, then a percent. Let us walk through this together
Since 5, and 40 have a common factor of 5 itself, we can divide 5 and 40 both by 5 thus,
5 / 5 = 1
40 / 5 = 8
So simplified 5/40 is equal to 1/8, now since 1/8 is a very common decimal in mathematics you will have to memorize that 1/8 = 0.125
NOW: To convert a decimal into a percent we multiply the decimal by 100, or move the decimal dot 2 places to the left.
So 0.125 x 100 = 12.5 %
Now this is a very useful trick and will be used often so make sure the master it.
As mentioned by others in the comments you can also use calculators for simple math such as this, some good online calculators that can help you through your mathematical journey include: MATHWAY. Com, wolfram alpha , and basic google