Answer :

The answer is y=5 when x=0.  5 times 0 is 0 which means the equation would be 3y=15.  3 times 5 is equal to 15 therefore y=5.
y= 5 because if you substitute 0 into x, you'll get 
5 times 0 + 3y= 15
5 times 0= 0 
Then, get 15-0=15
Finally, 15 divided by 3 will equal 5.