Linear Equation in two variables

A comparison of Company A and Company B’s mobile post-paid plans is given below. Study it and answer the related questions followed.
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Rahul purchased Company A’s plan and used it only for local calls and local SMS. He got a monthly bill of Rs 519. Sonali bought Company B’s plan and also used it only for local calls and local SMS. She got a monthly bill of Rs 500.

Form a linear equation in two variables for Rahul as well as Sonali, taking local calls minutes usage (outside the free limit) as x and local SMS sent as y.

Plot these two equations in Geogebra and using the graph answer the following questions:

a) If the number of SMS sent by both of them is 20 each, whose local calls usage(outside the free limit) is more and by how much? Name the coordinates of the points representing this situation.

b) If the number of local calls made by Rahul were within the Free usage limit, how many SMS were sent by him?

Check all that apply

c) If Sonali did not send any local SMS this month, how many minutes of local calls did she make so as to get to the amount mentioned in the bill?

Check all that apply

d) If you had to choose a plan, which one would you choose-Company A or Company B? Why?