Question 1174630

 {{{y=a+bx}}}

{{{y }}}denominates the telephone bill amount 
and 
{{{x}}} denominates the units consumed

given: 

when {{{x=200}}} unit were consumed the Bill amount was Tsh {{{y=2500000}}}

so we have

 {{{2500000=a+200b}}}.............eq.1

and when {{{500}}} unit were consumed the bill amount was tsh {{{y=4900000}}}

so we have

 {{{4900000=a+500b}}}.............eq.2


 to find {{{a}}} and {{{b}}} solve system


{{{2500000=a+200b}}}.............eq.1
 {{{4900000=a+500b}}}.............eq.2
--------------------------------------------------subtract eq.1 from eq.2

{{{4900000-2500000=a-a+500b-200b}}}

{{{2400000= 300b}}}

{{{b=2400000/300}}}

{{{b=8000}}}


go to

{{{2500000=a+200b}}}.............eq.1, substitute {{{b}}}
{{{2500000=a+200*8000}}} 
{{{2500000=a+1600000}}} 
{{{2500000-1600000=a}}} 
{{{a=900000}}} 


and, your equation is:

 {{{y=900000+8000x}}}