given that ∫15x^2 dx = 3430, and x=a and x=-a. Find the value of the constant a.

I'm not quite sure how to approach solving for a.

I(x) = 5x^3

So would I set that equal to 3430?

5x^3=5430

x^3=686

x= approx. 8.8?

The answer is that a=7.

7^3 is 343 ...

3430/10 = 343 .. but how could I get to that (justify it anyways)

Thanks so much, I really want to understand how to do this, I'm just confused on where to go from here.

Thanks!