Question r1150

My plan is to build a cascade system

First stage r290 running at evaporation -40

Second stage r1150 at around -80 (2.4 bar) evaporation

Condensation at -40^ (13.5) bar

My question is what would the pressure be at ambient temperature? For r1150 Around 20 degrees let’s say when the machine is turned off. The refrigerant slide goes to max 4.2 degree and that’s already 44.07 bar

Can’t find anything online. Thanks