David has earned the following test grades: 89, 96, 99, 85. What is the
grade David has to earn on his 5th test to maintain a test
average of 90?

81

Step-by-step explanation:

Required average= 90

let the required grade be x

Average= Sum of n numbers

90= 89+96+99+85+x divide by 5

450= 369+x

x = 450-369

x=81

-7

step-by-step explanation:

x^2 + 18x + 74 = (x + 9)^2 - 81 + 74

= (x + 9)^2 - 7.

so q = -7.

c.

step-by-step explanation:

because first you have to add the 4x, 9x, and the 7x together and you get 20x and then you add the last numbers up and you get 5and then you put the subtraction sign in there and that's how you get the answer.