First, we need to fond the LCM of 42 and 54. The LCM of 42 and 54 is 378.
Now, we shall find the difference of 42 and 34 which is 8. Similarly, the difference of 54 and 46 is also 8.
The difference of the LCM and 8 is the smallest number.
So, 378−8=370.
Hence, 370 is the smallest number when divided by 42 and 54 leave remainders 34 and 46 respectively.