3x-y=-15

3x=-15+y

3x+15= y

b is always the y intercept, so 15 is the y intercept

So

3x – 0 = 15

3x = 15

Now divide both sides by 3:

3/3 x = 15/3

1x = 5

x = 5

y = mx + c ………….(1)

then m gives the gradient and c is the y-intercept.

3x – y = -15

Add y to each side:

3x = y – 15

Add 15 to each side:

3x + 15 = y

Turn round:

y = 3x + 15.

Comparing with (1):

c = 15.

The y intercept is (0, 15).

-3x -3x subtract 3x from both sides

-y=-3x-15

you have to get rid of the negitive on the y by dividing by a negitive 1

-y=-3x-15

/-1 /-1

and your answer is y=3x+15

3x/3x-y=-15/3x

-y=-15/3x

-y=-5/x