How do you find the vertex & how do you know if a graph opens up or down asap

Standard form of a quadratic f(x) = ax^2 + bx + c
In a quadratic function you find the vertex using the formula x = -b/2a; once you find the x value, substitute it into the equation and solve for y.
To know if a parabola opens up or down you look at the coefficient of the x^2 term. If it is positive, the graph opens up; if it is negative, the graph opens down.

30000 feet

Step-by-step explanation:

temperature on ground level = 65 °F

temperature at cruising altitude = -43 °F

total decrease in temperature = 65 - (- 43) = 65 + 43 = 108 °F

for each 1000 feet elevation temperature drops by 3.6 °F

and we have the total drop of temperature as 108 °F.

so,  Height of plane at cruising altitude = (drop in temperature/ 3.6) X 1000

                                                                 =

                                                                 = 30000 feet