so first convet to slope intercept form which is y=mx+b where m is slope and b is y intercept
so since you are given x and y values and the slope, you can solve for b
so y=mx+b
y=1/4x+b
subsitute 12 for x and 9 for y
9=1/4(12)+b
9=3+b
6=b
so the equation is y=1/4x+6