Notice that the problem doesn't mention temperature or number of moles, which means that you can assume that they are being kept constant.
When this is the case, pressure and volume have an inverse relationship - this is known as Boyle's Law.
Simply put, when pressure increases, volume decreases, and when pressure decreases, volume increases.
This means that right from the start, you can look at the fact that the volume of the gas decreases and say that the pressure must increase.
Mathematically, this is expressed as
#color(blue)(|bar(ul(color(white)(a/a)P_1V_1 = P_2V_2color(white)(a/a)|)))" "#, where
Rearrange to solve for the pressure of the gas at the final state,
#P_1V_1 = P_2V_2 implies P_2 = V_1/V_2 * P_1#
Plug in your values to get
#P_2 = (6.00 color(red)(cancel(color(black)("L"))))/(1.40color(red)(cancel(color(black)("L")))) * "760 torr" = "3257.1 torr"#
Rounded to two sig figs, the number of sig figs you have for the initial pressure of the gas, the answer will be
#P_2 = color(green)(|bar(ul(color(white)(a/a)"3300 torr"color(white)(a/a)|)))#