To solve an equation or inequality, you can add the same value to both sides of the expression. Here, it is convenient to choose that value to be the opposite of the constant (+15) added to y, so that constant is replaced by zero.
y + 15 - 15 < 3 - 15 . . . . . we have added -15 to both sides
y < -12 . . . . . . . . . . . . . . . the result of simplifying. This is your solution.
Okay well, if you make a graph, Point A (7,0) and Point B (4,6) are in the top right quadrant. and Point C (1,1) and Point D (5,3) are in the top left, top right, and bottom left quadrant (I'll link a photo of the graph.)
so the lines intersect and make it perpendicular
The real way is to subtract the term with the variable on the right first, but both Spencer and Jeremiah are correct. When you do them both, they arrive at the same answer, only that Spencer's would be 2/5, and Jeremiah's would be -2/-5, which is 2/5, because you divide negative by a negative. It doesn't matter which term with the variable you would cancel out first. Either way, you still arrive at the correct answer.