Because this is a positive parabola, it opens upwards, like a cup, and the vertex dictates what the minimum value of the function is. In order to determine the vertex, I recommend completing the square. Do that by first setting the function equal to 0 and then moving the 9 to the other side by subtraction. So far:

. Now, to complete the square, take half the linear term, square it, and add that number to both sides. Our linear term is 6. Half of 6 is 3 and 3 squared is 9. So add 9 to both sides.

. The right side reduces to 0, and the left side simplifies to the perfect square binomial we created while completing this process.

. Move the 0 back over and the vertex is clear now. It is (-3, 0). Therefore, 0 is the minimum point on your graph. The first choice above is the one you want.
Answer:
4x+7 I believe but it could be wrong
Answer: 4.6 horas.
Step-by-step explanation:
Podemos calcular el tiempo necesario por una llave:
si sabemos que se llena en 8 horas con 4 llaves, entonces una sola llave va a tardar 4 veces 8 horas en llenar el tinaco, es decir, una sola llave tarda:
4*8h = 32 horas
ahora, si usamos 7 llaves, el tiempo necesario va a ser un septimo de eso:
(32 h por llave)/(7 llaves) = 32/7 horas = 4.6 horas.
Here's a tip Subtracting a fraction is the same as multiplying it's reciprocal so for 3/4 - 3/8 you can do 3/4 x 8/3. Multiplying its reciprocal mean turn the 2nd fraction around