20 points! i need somebody to explain this to me for D + 4 < 7.
i get the answer 3 but if it's 3 then at the end when im checking my work it ends up being D + 4 < 7
3 + 4 < 7
7 < 7 which is saying 7 is less than 7 ? what am i doing wrong

Assuming there is no line under the "less than" sign, this means D + 4 < 7 solves to D < 3, which is what I'm assuming you got. This is found by subtracting 4 from both sides.

Writing D < 3 means D is some number less than 3. A solution is just that. You cannot pick 3 itself because 3 is not less than 3. But you can pick something like 2 since it is less than 3.

D+4 < 7

2+4 < 7 ... replace D with 2

6 < 7 ... true

Or D could be 1

D+4 < 7

1+4 < 7

5 < 7 true

and so on.