Answer:
13.5
Explanation:
16x 9 = 144
x + (x+1) + (x+2)+ (x+3)+ (x+4)+ (x+5)+ (x+6)+ (x+7)+ (x+8) = 144
9x + 36 = 144
9x = 108
x = 12
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(12 + 13 + 14 + 15)/4 = 13.5
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