The volume of a gas with a pressure of 1.2 atm increases from 1.0 l to 4.0 l. what is the final pressure of the gas, assuming no change in moles or temperature?

Boyle's law gives the relationship between pressure and volume of gas.
for a fixed amount of gas, at constant temperature the pressure of gas is inversely proportional to its volume.
PV = k
where P - pressure, V - volume and k - constant
P1V1 = P2V2
where parameters for the first instance are on the left side and parameters for the second instance are on the right side.
substituting the values in the equation
1.2 atm x 1.0 L = P x 4.0 L 
P = 0.3 atm
new pressure is 0.3 atm

the catch is that the top numbers are atomic masses the bottom numbers are the numbers of protons and electrons in an uncharged atom. they are the number of that atoms as you would find them on the periodic table. further, the numbers on the left are used to determine the missing numbers on the right

so here we go

atomic mass

239 + 1 = y + 134 + 3 combine like terms

240 = y + 137             subtract 137 from both terms

240 - 137 = y

103 = y

atomic number

94 = z +54 + 0

94 = z + 54               subtract 54 from both sides.

40 = z

answer

Ibelieve y y even though i've only taken chemistry for one year