Help please i dont understand

13. $25/month

14. 36 and 37

Step-by-step explanation:

Let a = monthly rate ($/month)

t = time (months)

k = installation cost

The equation for the cost of the internet service C is

C = at + k

Since C = $685. t = 24 months (2 years) and k = $85, we can solve for a:

at = C - k

or

a = (C - k)/t

= ($685 - $85)/(24 months)

= $25/month

14. Let n = the number

n + 1 = the number after n

Since the sum of two consecutive numbers is 73, we can write the equation as

n + (n + 1) = 73

which simplifies to

2n + 1 = 73

2n = 72

Solving for n, we find that

n = 36

so the other number is 36 + 1 = 37.

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