Question#1
Y-3x+5

Moondown
y-3x+5 is not a line, dear.
I think you want to say
y-3x+5 = 0

If it is so, y = 3x - 5 ------ (I)
If m is the slope,
y= mx + c-------------------(II)
Compare I and II, we get -
m = 3, so slope is 3

To find the value of y-intercept, remember, it is the point, where x=0
So, fill x=0 in y-3x+5 = 0
and y-3(0)+5=0
y+5=0
y = -5
or, y+5=0 is the y-intercept.