Could someone tell me if this is correct

You are correct for 18a through 18c. Nice work.

18a. True (think of it as 21 is less than 27)
18b. False; 0.4 is the same as 0.40
18c. True. Three dollars is much greater than 20 cents
18d. False. 1.9 is the same as 1.90 and can't be smaller than itself
18e. False. The two sides are completely diferrent numbers.
18f. True. The value 6.2 is the same as 6.20

For problem 19, you have to make the denominators the same. So multiply top and bottom of the first fraction by 10 to go from 4/10 to 40/100

If 40 is in the first box, then 40+40 = 80 is the final numerator. If this is over 100, then 80/100 = 8/10 meaning that 10 goes in the other box.