Acceleration of a Hot Air Balloon

[Shepherd7]

Homework Statement

What is the magnitude of the acceleration of a rising hot-air balloon if the ratio of the air density outside the balloon to that inside is 1.25? Neglect the mass of the balloon fabric, the basket and it contents.

I don't know how to do a rho so "p" will be rho for density and P will be for pressure
o = outside of balloon
i=inside of balloon

po = 1.25pi
po (of air) = 1.2 kg/m^3
Po = 1atm = 101.3 kPa

Homework Equations

P+1/2pv^2+pgy = P+1/2pv^2+pgy
p = m/v
P=F/A

The Attempt at a Solution

I'm really stuck at the beginning of this problem. I can't seem to find any way to link density and acceleration (without time and a distance or and area). Any suggestions? Also are my assumptions about Po and po right? Seeing at I'm unsure of the elevation/air temp I can't be sure. Also are there other assumptions I should be making? Thanks!

 

[indr0008]

actually it is easier to draw the force diagram first :)