Question 934348
given:
A {{{4-min}}} call cost ${{{2.65}}} and a {{{10-min}}} call cost {{{4.75}}}. 

the linear equation: {{{y=mx+b}}} where {{{x}}} a number of minutes and {{{y}}} a cost, {{{m}}} a slope or in your case cost of a {{{1-min}}}call and {{{b}}} is y-intercept or in your case any additional fixed cost

if  {{{x=4}}} and {{{y=2.65}}}, then we have

{{{2.65=4m+b}}}.............eq.1

if  {{{x=10}}} and {{{y=4.75}}}, then we have

{{{4.75=10m+b}}}.............eq.2

sole this system to find {{{m}}} and {{{b}}}

{{{2.65=4m+b}}}.............eq.1
{{{4.75=10m+b}}}.............eq.2
______________________________..subtract eq.1 from eq.2

{{{4.75-2.65=10m+b-4m-b}}}

{{{2.1=6m}}}

{{{2.1/6=m}}}

{{{highlight(m=0.35)}}}

go to {{{2.65=4m+b}}}......eq.1 substitute {{{0.35}}} for {{{m}}} and find {{{b}}}

{{{2.65=4*0.35+b}}}

{{{2.65=1.4+b}}}

{{{2.65-1.4=b}}}

{{{highlight(b=1.25)}}}

so, your equation is:{{{y=0.35x+1.25}}}