Find a power function through the two points: (7,8) (1,0.7)

$\displaystyle f(x) = kx^p$

This is what I've gotten only:

$\displaystyle 8 = k7^p$

$\displaystyle 0.7 = k1^p$

I tried solving for p but it came out to be -1.25 and not 1.25 like the back of the book.

Thank you!