So for Qn 2
55 Tens
this 55 tens is a multiplication!
55 is the amount and tens are the group
let's say 55 gave ten dollars each, so we take 55 multiply 10 = 550

same for the next 2,
55 Hundredths
A hundred is 100
but a Hundredth is 1/100 (The difference is in the "th")
so we take 55 multiply 1/100 and acquire 0.55

55 Thousandths
A Thousand is 1000
but a thousandth is 1/1000 (The difference is in the "th")
So we take 55 multiply 1/1000 = 0.055

Qn 4,
so we have 3 Kg 60 g of mushrooms converted into grams would be 3060g
1490g of mushrooms used up
so we used the original amount and deduct the amount used up.

Hope this helps