Question: can x be a constant?
Answer: Your x can equal any number and your y can change depending on your x value. For example, if your x is equal 1, then your y is equal to 3 * 1 + 4 = 7. If your x is equal to 2, then your y is equal to 3 * 2 + 4 = 10. Then your x becomes a constant because the problem has stated that x is equal to 3.