Values and the golden rule
Rough values: chariot 9, cannon and horse about 4½ each, advisors, elephants and soldiers 1–2. The golden rule of exchanges (兑子): when you are AHEAD in material, trade pieces — every even swap leaves the ratio steeper. Red here is up a crossed soldier, so offering the chariots is exactly right: whatever Black recaptures with, the board gets simpler and the extra soldier gets louder. Make the offer.