Cartesian Planes - find the function that relates variables

[Guest]

Number of cars passing a point each minute varied linearly between 6:30 & 8:30. Reported 45 cars passing in one minute @ 7:00am while at 8:00am, 115 cars passed in 1 minute.

Assign variables to the number of cars passing the point in any minute and the number of minutes after 6:30am.

Find the function that relates the two variables.

[Guest]

Let 6.30 be time zero. Plot cars vertically. Plot half hour intervals horizontally
Plot the cars passing at half hour later ie 7.00
Plot the cars passing at 8.00 a further hour later.
get slope of line as change in cars divided by the time between
You get the eauation of the line to be
(Cars) = 35 x (Time) + 10 for half hour intervals
so cars at 7.00 = 35 x 1 + 10 = 45
and cars at 8.00 = 35 x 3 + 10 = 115

If you want in any minute....

at 7.30 ie 60 minutes after 6.30 = 35/30 x 60 + 10 = 80 cars

or at 7.50 ie 80 minutes after 6.30 = 35/30 x 80 + 10 = 103 cars