Which related equation can be used to solve the equation?
m + 5 = –7.3
a. m = –7.3 – 5
b. m = 5 – 7.3
c.
m = 7.3 – 5

It's A. m = –7.3 – 5.

You can always check it..

–7.3 – 5 = -12.3
-12.3 + 5 = -7.3

M+5=-7.3
m needs to be lone
move 5 to the other side of = sign dont forget to change sign
m=-7.3-5
no when two signs are the same we add
so its like saying 
m=-7.3+(-5)
m=-12.3 now lets check it
-12.3=+5=-7.3
-12.3=-5+(-7.3)
-12.3=-12.3 so we did it right

so your answer would be m=-7.3-5

C, e, and a (hope it )