SOLUTION: Ben's monthly phone bill includes a fixed charge, which is the same each month, and an additional flat rate charge for each long distance call. One month the bill was $32, which in

        Part 1

First, everything can be solved without any equations.


The difference between the two monthly bills is 38-32 = 6 dollars and 6-4 = 2 calls.


Hense, each call cocts 6/2 = 3 dollars.


Then the fixed monthly charge is  32 - 4*3 = 20 dollars (using the data of the 1st month).


So, the problem is just solved in this way.

        Part 2

With equations, let "a" be the fixed monthly charge and let "b" is the rate per one call.


Then the monthly cost equation is 

    C = a + bx.

where x is the number of calls.


You write it for two consecutive months

    a + 4b = 32,    (1)

    a + 6b = 38.    (2)


Then you subtract equation (1) from equation (2)

        6b - 4b = 38 - 32

           2b   =    6

            b   =    6/2 = 3.    Thus, in this part, you simply REPEAT
                                 operations, which I did mentally in the first part.


Having  b= 3,  you find "a" from equation (1) as

    a = 32 - 4*3 = 20.           Exactly as I did it in my first solution.