Hi there!
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We Know:
Freshman's Raised: $602
Sophomore's Raised: $186
Junior and Senior's Raised: ?
Total Raised: $1500
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Solution:
602 + 186 = 788
1500 - 788 = 712
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Answer: The Juniors and Seniors have to raise $712 to reach there goal of $1500.
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Hope This Helps :)