Study the groups. Write the smallest number? What is the difference between 150 and 105? What number is A?

The first group has 3 tens (rods), 2 tens (rows of blocks), and 4 ones (individual blocks).

The first number is 54.

The second group has 5 tens (rods), 2 tens (rows of blocks), and 6 ones (individual blocks).

The second number is 76.

Comparing 54 and 76, the smallest number is 54.

The final answer is $\boxed{\text{54}}$

16. What is the difference between 150 and 105?

The difference between two numbers is found by subtracting the smaller number from the larger number.

The final answer is $\boxed{\text{45}}$

17. What number is A?

The numbers given are 200, 195, A, 175, 170, ..., 150.
Observe the interval between consecutive known numbers:
$200 - 195 = 5$
$175 - 170 = 5$
The number line is decreasing by 5 for each step.

To find A, subtract 5 from 195.

The final answer is $\boxed{\text{190}}$

18. Look at Luvo's birthday cake. If his father is 30 years older than him. How old is his father?

To determine the father's age, Luvo's current age is needed. This information is not provided in the question.

The final answer is $\boxed{\text{Luvo's age is needed to solve this problem.}}$

19. Cathy reads 200 pages of a book. Mike reads 148 pages of the same book. How many more pages did Cathy read than Mike?

Cathy read 200 pages.
Mike read 148 pages.

To find how many more pages Cathy read, subtract Mike's pages from Cathy's pages.

The final answer is $\boxed{\text{52 pages}}$