A) 42,000m divided by 2 1/3 = 18,000m divide by 1000m to get km = 18km/hr
B) 18,000m divided by 60 to get minutes = 300m divide by 60 to get seconds = 5m/sec.
The speaker is the encoder. That is the correct answer B.
B=3; C=16; and E=4096.
Using the information we have gives us

We know that:

We know that 2³ = 8, so B = 3.
To "undo" a square root, we square the number; 4²=16, so C = 16.
To "undo" a fourth root, we raise the answer to the fourth power; 8⁴ = 4096, so E = 4096.
You have to simplify like this
(-5)(-8)=40