The pieces of equipment required to place 160 cubic yards of concrete in 1 day by experienced workmen are two gasoline engine vibrators and one concrete pump. If the vibrators cost $76 per day and the concrete pump costs $580 per day, the variable cost of the equipment per cubic yard of concrete is closest to: 

(a) $0.95

(b) $3.63

(c) $4.10

(d) $4.60