Question 1084005
x, time
y, cost


Points (9, 9.05) and (12, 10.4)


rate  {{{(10.4-9.05)/3=0.45}}}

{{{y=0.45x+b}}}
{{{b=y-0.45x}}}
{{{b=9.05-0.45*9}}}
{{{b=5}}}
-
{{{highlight_green(y=0.45x+5)}}}



30 minutes after the just traveled 9 minutes would be 39 minutes.
{{{y=0.45*39+5}}}
{{{y=22.55}}}



If the whole ride is only 30 minutes, {{{y=0.45*30+5=18.5}}}.