Please solve this Algebra 2 word problem

Question

Overseas phone call is charged at 1 rate (fixed amount) for 1st min and different rate for each additional min

7 min call costs: $10

4 min call: $6.40

Find each rate

Answer 1

Let F = fixed rate
 R = additional minutes rate

 

For 7 min call

 1Min Fixed Rate Balanced 6 min additional Rate

 So

F + 6R = 10________________eq 1

For 4 min call

1Min Fixed Rate Balanced 4 min additional Rate
So

F +3R = 6.40_________________eq 2

Subtracting eq 2 from eq 1:
F + 6R = 10

-F - 3R = -6.40
----------------
3R = 3.60
R = $1.20
.
To find F, substitute the above into equation 1 and solve:
F + 6R = 10
F + 6(1.20) = 10
F + 7.2 = 10
F = 2.8

 

 

Therefore:
Fixed rate is $2.8
Per minute charge after the first min is $1.20

Answer 2

Let B be the fixed rate (the intercept) and M be the rate per minute (the slope)

 

7 min call costs $10 ---->   B + 6M = 10

 

4 min call costs $6.40 --->  B + 3M = 6.40

 

subtracting the equations :  3M = 3.60

 

M = $1.20

 

B + 6*1.20 = 10

 

B + 7.20 = 10

 

B = 10 - 7.20 = 2.80

 

The first minute costs $2.80

Each minute thereafter costs $1.20

 

The function is C(t) = 1.20*t + 2.80 where t is the time in minutes