A linear function crosses the x-axis when x= -3 and the y axis when y = 12 Write the equation of the line.

y = m x + b       equation of straight line

If x = 0    then

12 = b    and we have y = m x + 12

If y - 0 then

0 = m (-3) + 12   and m = 4

y = 4 x + 12 is the final equation

Check:

let x = -3    then y = 0      as specified

-2

7 - 9 = -2

reversed:

-2 + 9 = 7