You have a 5.0 L balloon that you bought in Denver(0.85 atm). If you take
that balloon back to sea level, where the pressure is 1.0 atm, what will the
new volume of the balloon be?

New volume of the balloon at sea level (V1) = 4.25 L

Explanation:

Given:

Present volume (V) = 5 L

Present pressure (P) = 0.85 atm

Pressure at sea level (P1) = 1 atm

Find:

New volume of the balloon at sea level (V1) = ?

Computation:

According to  Boyles law:

⇒ P × V = P1 × V1

⇒ 0.85 × 5 = 1 × V1

⇒ 4.25 L = V1

New volume of the balloon at sea level (V1) = 4.25 L