Q.The marginal revenue is $MR=100-6x$. Find the total revenue function and the revenue from selling 8 units.

The same integrate-and-pin-at-zero procedure recovers the total revenue function from any marginal revenue function.

Integrating the marginal revenue

Pinning $K$ using $R(0)=0$

Revenue from selling 8 units

$R(8)=100(8)-3(8)^2=800-3(64)=800-192=608$ …

Computing $8^2$ as $16$ instead of $64$ — a simple squaring slip that silently propagates through the rest of the calculation; always do …