To find the zeroes of a function, you need to find the values of x that make y equal to 0. To do this, you need to plug 0 in for y and solve for x. After plugging 0 in for y, we have 0=3x+1. Then, we have to subtract 1 from both sides to get 3x=-1. Lastly, you need to divide both sides by 3 to get x=-1/3.
I hope this helps.