In order to achieve equilibrium, how many pizza slices can you consume if they are free of cost?

Til the time when MU = 0 

MU is the marginal utility which indicates the additional satisfaction derived from a commodity. Irrespective of the price, a person is motivated to consume additional units of a commodity only till the time he gets additional satisfaction, after that he stops consuming the product. So, the person will increase his consumption when MU is +ve and STOP when it becomes 0. Thus, it can be concluded that he will eat the slices till the point when MU = 0.