average of money that group of 4 friends pay for rent each month is $ 800 . after one persons rent is increased by 20 % the new mean is $ 870 . what was original rent of friend whose rent is increased ?
"0.2 x = 4 ( 870 - 800 ) 0.2 x = 280 x = 1400 answer b"
divide(multiply(subtract(870, 800), 4), divide(20, const_100))