You always begin by the Given equation, which is in this case:
y+

= 3x
To remove the fraction, you multiply the whole equation by 5:
5y + 1 = 15x
Then, you move the "15x" the left-side of the equation, changing it's sign
-15x + 5y +1 = 0
You move the "1" to the right side, changing it's sign
-15x + 5y = -1
So the correct answer is A :)
Hope it helped! ^^