Jennifer has a taco stand. she found that her daily costs can be modeled by c(x)=x^2-40x+610. if she wants to keep her daily cost at 300 dollars, how many units of tacos does she need to sell

Let's focus on the given equation. The C represents the cost, while the x must be the number of tacos, which is what we're solving for. Since we're given the boundary that C must be 300, then the solution would be:

300 = x² - 40x + 610
x² - 40x + 310 = 0

Apply the quadratic formula where a = 1, b = -40 and c = 310. The roots of x are:
x = 29.49≈30
x = 10.51≈11

Thus, she needs to sell either 30 or 11 tacos.