Hello.
Isolate the variable in order to make it the subject of the equation:
v=4+y
Subtract it from both sides:
v-y=4+y-y
v-y=4
Now, subtract v from both sides:
v-v-y=4-v
-y=4-v
Get rid of the minus sign:
y=-4+v
Or

I hope it helps.
Have an outstanding day.
