I would half 198, get
99 and add a 0, this is how you multiply by 5 in your head
1985 = 990
990 + 200 = 1190 - 2
= 1188
Alternatively we can round 198 to 200: then multiply by 6
2006 = 1200
Then We subtract the 6 "2's" that we added
1200 - 12 = 1188
The expression for this is:
(6200) - (6 2)
