Question 84538
The point (-3,y) means that we have an x value that equals -3 and an unknown y value. So to find the unknown y value, plug in x=-3


{{{y = -3(-3) + 4}}} plug in x=-3


{{{y = 9 + 4}}} Multiply


{{{y = 13}}} Add 


So the y value equals 13. In other words, the point (-3,13) lies on the line {{{y = -3x + 4}}}


Here's a visual verification:


{{{drawing( 900, 900, -10, 10, -5, 15,
  grid( 1 ),
  graph( 900, 900,-10, 10, -5, 15, -3x+4),
  circle(-3,13,0.05), 
  circle(-3,13,0.08)
)}}} graph of {{{y = -3x + 4}}} with the point (-3,13)