Question 548676
 C = 0.25(t - 600)+ 73.95 solve for t? if cost is between $123.95 and $143.95 that is  {{{123.95 < C < 143.95}}}
Therefore:
 {{{123.95 < 0.25(t - 600) + 73.95 < 143.95}}}
 {{{123.95 < 0.25t - 150 + 73.95 < 143.95}}}
 {{{123.95 < 0.25t -76.05 < 143.95}}}
 {{{123.95 + 76.05 < 0.25t < 143.95 + 76.05}}}
 {{{200 < 0.25t < 220}}}
{{{200/0.25 < t < 220/0.25}}}
 {{{800 < t < 880}}}
Hence,the telephone time must be between 800mins and 880mins in order for the cost to be between $123.95 and $143.95