For a. Isolate the y value. So -3y=8. Multiply both sides by -1/3, so y equals -8/3
For b. I would multiply the entire equation by 3 to get rid of the fraction. So the new equation is now -2t-6=-9. Isolate the variable, t, again. So it is now -2t=-3. Multiply both sides by -1/2, and t=3/2
For c. Nothing seems to be wrong except for the fact that you forgot a negative sign in one of the steps