Question 814686
x = lean price, y = cost
y=(1-0.10)x   cost is (100%-10%) times x
y=0.90x

for regular hamburger
y=(1-0.30)1.09   cost is (100%-30%) times $1.09
y= 0.70*1.09
y= 0.763

So when 0.90x = 0.763 lean and regular would have the same value.
            x= 0.763/0.90
            x=0.8477