Question

the charge for telephone call ,t,partly constant and partly varies with the number n of call. the bill for 420 units of call is 806,while the bill for 200units is 410
A)calculate the charge for 460 unit of electricity
B)find a formula for T

Answer 1

so t = nk + c, where n is the number of calls
your given information yields the following pair of equations:
806 = 420k + c
410 = 200k + c
subtract them:
396 = 220k
k = 9/5 = 1.8

sub into 410 = 200k + c ---> c = .....

and you got your equation. B)
plug in n = 460, and evaluate t

Answer 2

How is n 460

Answer 3

That's great