5/7y=3-1/5 what is y?

You want y? One way to get y alone would be to mult. all 3 terms by (7/5):

(7/5) (5/7) y = (7/5) * 3 - (7/5) (-1/5). This simplifies to:

y = 21/5 * 7/25, or y = 147 / 125.

You could check this using decimal fractions:

y = 4.20 * 0.28 = 1.176 = 147 / 125.