Question

17 and 18 with work. Getting confused

Answer 1

#18:
work out the top part first: 
a/(a(a+h) -(a+h)/a(a+h)=-h/a(a+h)
the top divided by the bottom is equivalent to the top × 1/the bottom:
-h/a(a+h)*1/h=-1/a(a+h)
the numerator is -1, the denominator is a(a+h)