Ineed with questions 15, 17, 18, and 19

Question 12 : Answer is C

Given that the equation is y = -3x + 6
Matching it to the general equation y = mx + c
slope = -3 


Question 14: Answer is C

Given that the equation is y - 2x = 4
y - 2x = 4
y = 2x + 4
Matching it to the general equation y = mx + c
slope = 2 


Question 15: Answer is B

y = -2x + 1
Given that the equation is y = -2x + 1
Matching it to the general equation y = mx + c
slope = -2 


Question 17: Answer is D

Equation: x = 3 
x = 3 is a vertical line, Gradient is undefined.


Question 18: Answer is C

When gradient is 0, it means there is no slope.
Then it has to be a horizontal line.
Among the answer, y = 3 is a horizontal line that cuts the y-axis at (0,3)


Question 19: Answer is A

When gradient is 0, it means there is no slope.
Then it has to be a horizontal line.
Among the answer, y = 1 is a horizontal line that cuts the y-axis at (0,1)

The answer is the third choice

The right answer should be 6 but your not very specific