Which equation can be used to find the answer?

After two months, Rachel has saved enough money to buy an MP3 player. During the second month, she saved $87 and she pays $199 for the MP3 player.

How much did Rachel save during the first month?

A.
m = 87 • 2
m = 174
$174

B.
199 + 87 = m
m = 286
$286

C.
m + 87 = 199
m = 112
$112

D.
m – 87 = 199
m = 287
$287