Answer:
x > 1.7 minutes
The monthly telephone usage amounts so that plan A is not greater than plan B are all greater than 1.7 minutes.
Step-by-step explanation:
The two plans must be defined by the equation of the line y = mx + b, where
y = plan
m = slope or payment of additional cents per minute
x = time expressed in minutes
For Plan A, we have
y = 4x + 40.10 (Equation A)
While plan B is defined as
y = 7x + 35 (Equation B)
Plan A must be less than Plan B,
4x + 40.10 < 7x + 35
We put the “x” on the left side and the independent terms on the right side,
4x - 7x < 35 - 40.10
We add algebraically,
-3x < -5.10
We multiply the equation by -1 to eliminate the two “minus” signs, changing the inequality sign,
3x > 5.10
We isolate x,
x > 5.10 / 3
We solve, calculating the value of x,
x > 1.7 minutes
The monthly telephone usage amounts so that plan A is not greater than plan B are all greater than 1.7 minutes.
is symmetric if 
. We have
is indeed symmetric.