Why is the y intercept a negative number and I get a positive number

Question

Taking a test earlier my problem was:

Find the slope and y-intercept of

9x=10y+40

My answers were slope =9/10 y intercept =4

The slope was correct but the y intercept was -4 instead of 4.

Why is the y intercept a negative number when I get a positive number as the solution?

Answer 1

the equation must be in the form y=mx+b

9x=10y+40

subtract 40 from both sides

9x-40=10y

rearrange sides

10y=9x-40

divide both sides by 10

y=(9/10)x-4

the slope is 9/10

the y-intercept is -4 not +4