Answer :
You should regroup when the product of the two numbers are greatre than nine so 378*6 6*8 is 48 so you would the 8 and regroup the 4 and do the same thing for the rest of the numbers if the product is greater than nine. Your answer will be 2268.
Expand 378 as (300+70+8) then multiply it 6. It will be (300 x 6)+(70 x 6)+(8 x 6)=
1800+420+48=2268