C(x)=2100+150x+10x2, R(x)=200x+200x2.
C(x+1)=2100+150(x+1)+10(x+1)2=2100+150x+150+10x2+20x+10;
R(x+1)=200(x+1)+200(x+1)2=200x+200+200x2+400x+200.
Marginal cost, Cm=C(x+1)-C(x)=150+20x+10=160+20x;
marginal revenue, Rm=200+400x+200=400x+400.
Marginal profit=Rm-Cm=400x+400-(160+20x)=400x-20x+400-160=380x+240.