Could you with this question and explain how to find the answer? ?

Your only option is to fill in the given points. That will give you two equations from which you can work out k and a.

Fill in (1,7) gives the easy formula 7 = k·a
Fill in (3,175) gives 175 = k·a·a·a

If you replace k·a in the second one with 7, you get:

175 = 7·a·a => a²=25 => a=5

Fron this and the first eqn follows k=7/5