Step 1 :The profit function is a quadratic function. The maximum value of a quadratic function is at its vertex. The x-coordinate of the vertex of a quadratic function given in the form \(f(x) = ax^2 + bx + c\) is \(-b/2a\).
Step 2 :In this case, \(a = -0.12\) and \(b = 41\), so the number of grills they'd need to sell to make the largest possible profit is \(-41/(2*-0.12)\).
Step 3 :Calculate this value and round it to the nearest ten.
Step 4 :The calculation gives us an x value of approximately 170.83333333333334.
Step 5 :Rounding this to the nearest ten gives us 170.
Step 6 :Final Answer: The company needs to sell approximately \(\boxed{170}\) indoor grills to make the largest possible profit.