Question 639747
Given
(1) 5x - 4y = 20
To find the pair of coordinants that satisfy this equation substitute the given coordinate into the given equation and solve for the other.
a) when x = 0, we have
5*0 - 4y = 20 or
-4y = 20 which yields
y = -5
Now check your answer.
Is (5*0 - 4*(-5) = 20)?
Is (20 = 20)? Yes
The solution pair is (0,-5) as you rightly found.
b) when y = 0, we have
5x - 4*0 = 20 or
5x = 20 which yields 
x = 4
Now check your answer.
Is (5*4 - 4*0 = 20)?
Is (20 = 20)? Yes
The solution pair is (4,0)
c) When y = -10, we have
5x -4(-10) = 20 or
5x = 20 - 40 or
5x = -20 which yields
x = -4
Now check your answer.
Is (5*(-4) -4(-10) = 20)?
Is (-20 + 40 = 20)?
Is (20 = 20)? Yes
The solution pair is (-4,-10)