Unique public static IP on VPN

Good morning everyone
I’m new to the forum and I would like, if I may, to explain my problem to you.

I have 2 offices (main office A and branch office B) connected to each other via VPN (IP tunnel + IPSec)
with each their own static public IP, through an RB1100 (Main) and an RB750Gr3 (detachment).

I would need office B to go out on the internet with the static public IP of office A, unfortunately
I can’t find a line to follow in order to at least carry out some tests.

can you help me?

Thank you

One line answer a slash /30 transit on the ip tunnel ends and add a static routes to each router

Details

OFFICE A TUNNEL END ============= OFFICE B TUNNEL END
10.55.55.1/30 … 10.55.55.2/30

You should be able to ping each router from other via 10.55.55.xxx
Then just static route traffic thru transit IP’s

So on Office B static route everything to Office A
static route 0.0.0.0/0 nexthop 10.55.55.1
You want traffic from office B LAN bbb.bbb.bbb.bbb to NAT out thru Office A
So anything that can’t route locally on Office B will now be passed thru to Office A (usually internet)

So on Office A static route the private IP of Office B back to it
static route bbb.bbb.bbb.0/24 nexthop 10.55.55.2
Anything coming back from a NAT but with Office B LAN address must go back to Office B

Thank you for your answer.
Today I’ll try to make the changes and I’ll update you on the results

Also consider wireguard VPN instead of ipsec.