There was a total of 21 math books in the two drawers of Mrs. Luca's classroom desk, including the 8 books she found in the bottom drawer. Which equation can be used to find b, the number of books that were in the top drawer?
A. b ÷ 8 = 21
B. b − 8 = 21
C. 8b = 21
D. b + 8 = 21

1.4

2.3

step-by-step explanation:

the formula for the constant of variation is

y= kx

divide each side by x

y/x =kx/x

y/x =k

we know a and y

1.   y/x = k

4/1 =4

check the other values to make sure they are the same

8/2 = 4   12/3 =4   and 16/4 =4  

the constant of variation is 4

2.   y/x = k

3/1 =3

check the other values to make sure they are the same

6/2 = 3   9/3 =3   and 12/4 =3  

the constant of variation is 3

answer4 to the second power is 16

and 4 to the third power is 64,