Question 1045240
set the two equal to each other, for then it is in equilibrium.
-0.1x^2-x+40 =0.1x^2+2x+20, put everything on the right.
0=0.2x^2+3x-20
multiply everything by 5 to make the x^2 leading coefficient 1.
0=x^2+15x-100
0=(x+20)(x-5)
x=5, since x can't equal -20
That is 500 watches since x is hundreds.
now substitute into both, since they should be the same to check
-2.5-5+40=$32.50
2.5+10+20=$32.50
That is 500 watches at $32.50 each for the equilibrium price.
{{{graph(300,300,-10,10,-10,50,-0.1x^2-x+40,0.1x^2+2x+20)}}}