Set u= 5x therefore u2=25x2. When you do that you can use substitution and say u =5x du = 5 dx or dx=du/5.
You will get something like the ∫ 1/(1+u2) du/5
To integrate this look at your table of integrals to find out this is an arc tan and when you integrate it you will get 1/5 arctan u + c. Substitute 5x back for you and you have the answer. Now plug in the numbers to get the final result.