A restaurant sells a coffee refill mug for $6. Each refill costs $2. Last month Keith spent $30 on a mug and refills. Write an equation
you can use to find the number of refills Keith bought. Use x for
your variable and do NOT type and spaces. *

First locate the turning point (vertex) of the graph. which is at the coordinates x=5 and y=9 or (5; 9).to determine whether it's a maximum or mininum value, you have to discern whether the vertex's y-value is the highest value or lowest value the graph can reach. since the vertex's y-value, 9 is the highest value the graph can reach, it will be a maximum.another basic way to determine whether the vertex's value is max or min is to see if the graph is smiling or sad. if it's smiling, the turning point/vertex would be a minimum, while a sad parabola would have a maximum y-value at the vertex.