Okay, I'll give it a shot. Painting A was dated 1604 and Painting B was dated 802.
If (in 2005) the first painting is three times older than the second, then:
And if the numerical value of the date on A is twice that on B, then:
So we have an equation for A in terms of B, let’s substitute it into the first equation and solve for B
And two times 802 is 1604.
And the age of B is 2005-802=1203years which is three times the age of A: 2005-1604=401years