What value of the variable makes the statement true? m+4 = –2.8
a. –6.8
b. –1.2
c. 1.2
d. 6.8

The value of the variable that makes the statement true is 

a) -6.8

This is because if you plug it back into the equation, you get -6.8 +4 = -2.8.  Then, if you combine like terms on the left side of the equation, you get -2.8= -2.8, which is a true statement.