Question 80718
To see which solutions make {{{x-y=4}}} true, simply plug in the possible solutions into x and y:

Lets plug in (0,4)


{{{0-4=4}}}

{{{-4=4}}} not true. So this eliminates answer a)


Now lets try b)

Plug in (-4,0)

{{{-4-0=4}}}

{{{-4=4}}} not true. So this eliminates answer b)


Now lets try c)

Plug in (0,-4)


{{{0-(-4)=4}}}

{{{0+4=4}}}

{{{4=4}}} true

Now lets plug in (-3,-7)

{{{-3-(-7)=4}}}

{{{-3+7=4}}}

{{{4=4}}} true. So this means c) is an answer.


For the sake of the problem, lets try d) as well

Plug in (3,1)


{{{3-1=4}}}


{{{2=4}}} not true. So this eliminates answer d)



So the only answer that satisfies {{{x-y=4}}} is answer c)