For x including [–15, 13] the function f is defined by f(x)=x^7(x+4)^6?

For x including [–15, 13] the function f is defined by
f(x)=x^7(x+4)^6

On which two intervals is the function increasing (enter intervals in ascending order)?

( i was able to get the first interval but had problems with the first number on the second. I thought it was zero but its wrong)

1.( -15 to -4)
and
2. (???? to 13)