Question 909082
1/3,4/5,-5/7,1/4,
y=21/40x+b
find b
4/5=21/40(1/3)+b
b=5/8
y=21/40x+5/8
y=21/40x+25/40
This is slope intercept form
The question asks for standard form.Ax+By=C
So to convert:
Multiply by 40 to get rid of fractions
40y=21x+25
Move y to other side
0=21x-40y+25
Move constant to other side
21x-40y=-25
Now it is in standard form.Ax+By=C
Now to check the answer by plugging in both sets of points.

check

My answer
Substituting x and y
21x-40y=-25
Using point -5/7,1/4
21(-5/7)-40(1/4)=-25
-15-10=-25
-25=-25 TRUE
Using point 1/3,4/5
21(1/3)-40(4/5)=-25
7-32=-25
-25=-25 TRUE

Other tutors answer
63(1/3)-4/5=-75
21-4/5=75
20 1/5=75 FALSE 
63(-5/7)-1/4=-75
-45-1/4=75
-46 1/4=75 FALSE
Conclusion: His answer is wrong!