On the right side, there are
• 2•2 = 4 atoms of Nb
• 2•5 = 10 atoms of O
so among the reactants on the left, the reaction is balanced as
4 Nb + 5 O₂ → 2 Nb₂O₅
Let 0.25x is the price increase. Therefore, the number of attendees will be 350-10x and the revenue R=(350-10x)*(5+0.25x)=1750+37.5x-2.5x^2. This parabola has maximum at x=10, meaning the price=7.5
When y varies inversely as x ⇒ y*x=k
y=27 and x=40 ⇒27*40=1080=k
y*10=1080
y=1080:10
y=108
