Answer:
use phythagoras formula of calculating right angles
a^2=b^2+c^2
42^2=b^2+78^2 (substitution + transposement)
b^2=72^2-42^2
b^2=3420 (introduce a square root both sides)
what you do on the left .you also do it on the right
b is the unknown side of the triangle
b=58.48 inched
