Question

Write an expression that can be used to multiply 6x198 mentally

Answer 1

You could multiply
6 times 100

then 6 times 90 or 6 times 9 then add zero

and finally 6 times 8

then add them all together

i don't think its what you want but this is what i would do. mentally

Answer 2

6×100+6×90+6×8 I think that is the answer