Question 146518
C=0.6xsq-140x+6200
R=-0.4xsq+130
profit=revenue-cost. 
10,000=-.4x^2+130-(0.6x^2-140x+6,200)
10,000=-.4x^2+130-.6x^2+140x-6,200
x^2-140x+10,000-6,200-130=0
x^2-140x+3,670=0
using the quadratic equation we get:{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}} 
x=(140+-sqrt[-140^2-4*1*3,670/2*1
x=(140+-sqrt[19,600-14,680)/2
x=(140+-sqrt[4,920]/2
x=(140+-70.14)/2
x=(140+70.14)/2
x=210.14/2
x=105.07 answer.
x=(140-70.14)/2
x=69.86/2
x=34.9 answer.