Yes because if not people wouldn't understand how did you calculate electric field strength.
In a series circuit the total current is the same throughout resistors and so:

The voltage is distributed throughout the resistors and so:

and the total resistance can be calculated by adding up the resistors resistance:

First thing is to calculate the total resistance and so:

And by Omh's law V=IR we have:

And so the total current of the circuit is 1.2 amps i.e. 1.2 A.
The frequency of the wave is 6800 Hz
<u>Explanation:</u>
Given:
Wave number, n = 20
Speed of light, v = 340 m/s
Frequency, f = ?
we know:
wave number = 

Therefore, the frequency of the wave is 6800 Hz