Answer
$y'=(1-x/7)^{-8}$
Work Step by Step
Find y and u:
$y=u^{-7}$
$u=1-x/7$
First, find the derivative of y and u. Don't forget to apply chain rule for y':
$y'=-7u^{-8}\times u'$
$u'=-1/7$
Then plug in u and u' into y':
$y'=-7(1-x/7)^{-8}\times-1/7=(1-x/7)^{-8}$
