Answer:
1/r^56
Explanation:
Not sure if you did a typo there or what cus 7 x 8 should be 56
Whenever the power of a number is negative, you flip. So r^-7 becomes 1/r^7
Remove the bracket and distribute 8 to the power of 1 and r^7
1 to the power of 8 will still be 1, r^7 x 8 = r ^ 56