The number of more friends that Bobby need to call to help finish cleaning in time is 20 friends.
Let x represent number of more friends
Number of hours=8×(9+1)
Number of hours=8×10
Number of hours=80 hours
Hence:
10×2+2(10+x)=80
20+20+2x=80
Collect like terms
2x=80-40
2x=40
Divide both side by 2x
x=40/2
x=20 friends
Therefore the number of more friends that Bobby need to call to help finish cleaning in time is 20 friends.
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