Christina buys 3 DVDs . 2 of the DVDs cost X+Y . Write an expression that shows the amount the 3 DVDs cost

3×(18−d)=54−3d

Step-by-step explanation:

The cost of one dvd is (18-d)(18−d) .

The cost of three dvds is 3×(18-d)=54-3d3×(18−d)=54−3d

a 4/6 = 9/12   not proportional

step-by-step explanation:

to find which are not proportional, we can use cross products

if it is true, they are proportional.   if it is not true, they are not proportional.

a 4/6 = 9/12

4* 12 = 6*9

48 = 54

not this is not proportional  

b 2/3 = 12/18  

2* 18 = 3 * 12

36 = 36

this is proportional

c 5/4 = 10/8  

5*8 = 4*10

40 = 40

this is proportional

d 7/5 = 35/25

7*25 = 5 * 35

175 = 175

is proportional