here is my equation that I am struggling with (7-42a)(-3/7) the 3/7 is a fraction.

Just multiply -3/7 by each member of the term; i.e.,
7(-3/7) - (42a)(-3/7)=
-3 + (6a*3) = can you take it from here?

(7-42a)(-3)= -21+126a is the Numerator
and 7 is the denominator