A)
Multiplying 2.5 and 1.4.
2.5 has one decimal place and 1.4 has one decimal place
The result of multiplication should have 1+1=2 decimal places.
Hence the answer is 3.4.
B)
Multiplying 0.64 and 0.81
0.64 has two decimal places and 0.81 has two decimal places.
The result of multiplication should have 2+2=4 decimal places.
Hence the answer is 0.5184.