Question 490210
you will use:
A common form of a linear equation in the two variables {{{x}}} and {{{y}}} is

    {{{y = mx + b}}}

where {{{m}}} and {{{b}}} designate constants. 




let num of Tapes be {{{x}}} (independent variable) and
total cost {{{y}}}(dependent variable)



so, we have


1.
{{{y= 8.50*x}}}


2.

{{{y= 17.00*x}}}


3.

{{{y= 25.00*x}}}


4.

{{{y= 34.00*x}}}