How can I use the download from a line and the upload from another line at the same moment ?

RouterOS Beginner Basics
1

Excuse me
Can you help me please
I have two internet line , A is the first with : 100M download and 2M upload
and B is the second : 20M download and 100M upload
How can I use 100M download from A and 100M upload from B at the same moment
please

2

You can make use of the mangle facilties in the firewall.
As long as the source and destination for both streams are different.
Look at the PCC samples on the web and alter it in order to force certain communication over a dedicated line.