Ok, so the starting numbers are the fixed amounts. If we think of a graph, this is the y-intercept/ starting point and the rate would continue from there. This conclusion is very important to writing a linear equation in slope-intercept form.
If you don’t remember, slope-intercept form is y=mx+b, where m is the slope and b is the y-intercept.
First, let’s make our equations.....
Plan A: y = 0.07x + 26
Plan B: y = 0.12x + 17
Now since it is not stated, I’m not sure if you need to find where the cost of both plans is equal, but that would be found by setting up a system of equations and using substitution.
y = 0.07x + 26
y = 0.12x + 17
Substitute one equation into the other...
0.07x + 26 = 0.12x + 17
- 0.05x = -9
0.05x = 9
x = 180
And there you have it! After 180 minutes [3 hours] of talking, both phone plans will have the same cost.
