<PRE><B>Question 83917</B>
If there was a $50 loss, then {{{P=-50}}}


{{{-50=x^2-13x-80}}} Plug in {{{P=-50}}}. Now lets solve for x


{{{0=x^2-13x-80+50}}} Add 50 to both sides


{{{0=x^2-13x-30}}} Combine like terms


{{{0=(x+2)(x-15)}}} Factor the expression


{{{x+2=0}}} or {{{x-15=0}}} Set each factor equal to zero


{{{x=-2}}} or {{{x=15}}} Solve for x in each case


Since you cannot sell -2 watches, the number of watches sold was 15</PRE>