If One Worker Can Pick $30 Worth of Grapes and Two

If one worker can pick $30 worth of grapes and two workers together can pick $70 worth of grapes, the

A) marginal revenue product of each worker is $35.
B) marginal revenue product of the first worker is $40.
C) marginal revenue product of the second worker is $40.
D) data given are insufficient to determine the marginal revenue product of either worker.