Aballoon contains 0.5 l of air at 101.5 kpa. you squeeze it to a volume of 0.25 l. what is the pressure of air inside the balloon? assume the temperature and amount of gas remain constant.
a.50.8 kpa
b.0.25 kpa
c.102 kpa
d.203 kpa

Pressure and volume are inversely proportional. 
When one increases the other decreases and vice versa. 
If you think about it, what have you done by squeezing the balloon to a smaller volume? you have brought all the atoms closer, thus they are more likely to collide and have less space to move around. 
What is pressure? well, pressure is just the force that atoms apply on the walls of the container(in this example , the container is the balloon)
So by decreasing the volume, you have increased the  pressure. 
By halving the volume, you double the pressure. 
OPTION D

1. and 2. question: in which equation? or i don't understand you, 3. a), 4. c), 5. c), 6. b), 7. d), 8. d) if small number is underlined(behind symbol) , b) if big number is underlined(in front of symbol)9. what is underlined there? 10. c)