A:
The first number is the magnification. These are fixed power scopes so the 3.5x40mm scope will have a magnification of 3.5 times normal eye sight. So something 350 yards away would look like it was 100 yards away. (4.5x40mm would be 4.5 times greater magnification than normal eye sight).
The second number refers to the diameter of the bell (the far end of the scope). The 3.5x40mm scope has a bell diameter of 40mm. The larger the diameter of the bell the more light it can capture, meaning in a hunting situation you will be able to see better in low light (dusk and dawn). The advantage of more light is more pronounced at higher magnifications and long ranges, so with these 4 scopes I don't think you would notice too much difference.
The advantage of a 30mm tube is also more light. The larger the diameter of the tube, the more light can travel through, the better a shooter can see in low light situations. Also the 30mm tube allows for more vertical and horizontal adjustments for long range shooting. Hope this helps.