But why does it still need on I need to pay for my subscription?

there is no possible way mgk stands a chance with the greatest white rapper of all time. eminem killshots had more bars than rap devil and the reason mgk is doing all this is cause he not getting attention anymore til the release of rap devil and the disses he is putting on eminem. now rap devil was more fire than killshot so mgk might won the battle with rap devil but eminem won the war with killshot.

answer: marginal utility of the fourth brownie is 0.

explanation: marginal utility is the addtional utility gained from the consumption of one more unit of a good. it is given by,

so, marginal utility at the 4th unit will be given by

since, the values are not given here, you can simply find marginal utility at fourth unit by subtracting total utility at 3rd unit from total utility at 4th unit.