In this problem, How do I go from TR to MR? It looks like im dropping the Q but how do I go from .8 to .16?

P=a+bQ

a=Y intercept=Maximum price consumers are willing to pay

a=$160

b=slope=change in P/Change in Q

b=(152-160)/(10-0)

b=-8/10

b=-0.8

P=160-0.8Q

ii)

TR=P*Q

TR=(160-0.8Q)*Q

TR=160Q-0.8Q²

MR=TR/Q

MR=160-0.16Q