Well in order to find the slope the equation should be in y= mx +b format, where m=slope to do this you take your equation, 7x=-3y+15 and notice how the x and y are in the wrong position , add the 3y to both sides and subtract 7x from both sides 7x=-3y+15 +3y +3y 7x+3y=15 -7x. -7x 3y=-7x+15 now we need the y to be by itself so we divide the entire equation by 3 and get y=-7/3x+5 so -7/3 or 2.33 or 2 1/3 would be the slope, the slope of parallel lines are equal
which applies to a right triangle. I hope that helps you.