Plug in 300 for C(x), to get:
300=[tex] x^{2} -40x=610[/tex]
Then subtract to get: 0=[tex]0= x^{2} -40x+310[/tex]
Then use the quadratic formula and plug everything in. Use a calculator to simplify.
You'll get two answers: 29.486 and -0.513.
Since you can't sell "negative" tacos, use the positive solution
Around 29-30 tacos.
