To get the total resistance in a parallel circuit, you need to remember that unlike in a series, you do not just merely add the resistances. You need to get the reciprocal first of each resistance and add them together.

After adding them, you will get the reciprocal again and then compute for the value. The problem says that there are 4 resistors in the circuit that have a resistance of 75.

Add up the numerator and copy the denominator:

Then get the reciprocal to get the total resistance:

The answer to your question then is A. 18.8.
football hemets have pads that are filled with air and thick foam so when they are hit the foam asorbs the hit and the air keeps the hard outer shell of the helmet from hiting the players head
For radio broadcasting, in electricity meters, in any generator.
The air would contract therefore the answer is the second choice.