Harvey mows lawns in his spare time for extra income. buyers of his service are willing to pay $50 per lawn for as many lawns as harvey is willing to mow. on a particular day, he is willing to mow the first lawn for $25, the second lawn for $30, the third lawn for $45, and the fourth lawn for $60. assuming harvey is rational in deciding how many lawns to mow, his producer surplus is

a) $40.
b) $10.
c) $25.
d) $50.