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he's not correct.

-15 = m

Step-by-step explanation:

-16 = -1 + m

-16 + 1 = m

-15 = m

Why does -1 became +1 , It is because you are adding 1 on both side so that we can cancel out the -1 and it will rest the m.

like this;

+1 -16 = -1 + m +1

-16 + 1 = (0 or nothing) + m

-15 = m

a and c

step-by-step explanation:

47 - 90 = 43

43 - 180 = x

x = 137