You are given the problem x + 3 = 7.
Let's go to Integer Bars Java Program by Jacobo Bulaevsky to see what this really means.
It was 4!
Now, let's check the addition. Is 4 + 3 really equal to 7? YES! So, we solved for x correctly.
Using the Integer Bars Java Program try these:
x + 2 = 6 y + 10 = 12 a + 2 = 9
Once you have tried them, look here to check your answers.