what is the y-intercept of [(4,5) and (4,-4)],[(-4,-3)and (6,-3)],[(-5,-7)and(8,1)],[(-6,6)and(7,3)]
the first line is vertical: x=4. So, no y-intercept there.
the 2nd line is horizontal : y = -3. So, duh - the y-intercept is -3
Always watch for such trick questions.
For the other two, figure the slope and see how far y changes when you pick a point and change x to zero.
For example, the slope of the 3rd line is 4/11.
So, when x changes from -5 to 0 (+5), y changes by 4/11 * 5 = 20/11. -7 + 20/11 = -57/11
Or, more formally, you can use the point-slope form and then solve for y when x=0.
y+7 = 4/11(x+5)
y+7 = 4/11(0+5)
y = 20/11 - 77/11 = -57/11
I'll let you do the last one.