How to calculate power in series and parallel circuit?

Hint :We can define power as the rate of doing work; it is the amount of work done in a given amount of time. Watt (W) is the SI unit of power, which is joules per second (J/s). Horsepower (hp), which is approximately equal to 745.7 watts, is sometimes used to describe the power of motor vehicles and other machines.

Complete Step By Step Answer:
In a series circuit, all components are connected end-to-end, forming a single path for current flow. In a parallel circuit, all components are connected across each other, resulting in exactly two sets of electrically common points.
The total power in a series circuit is equal to the SUM of the power dissipated by the individual resistors. Total power (PT) is defined as: PT = P1 + P2 + P3... Pn. As an example: A series circuit is made up of three resistors with resistance values of 5 ohms, 10 ohms, and 15 ohms.
A parallel circuit has the same voltage across each branch that is equal to the source voltage. The current flowing through a parallel branch is proportional to the resistance of the branch.
To determine the equivalent resistance $ \operatorname{Re} $ of a parallel or series circuit.
Any circuit's power we have one formula,
 $ \begin{align}
  & ={{\left( Electric\text{ }current \right)}^{2}}\left( Electric\text{ }resistance \right) \\
 & ={{I}^{2}}Re \\
 & \\
\end{align} $
Where, $ I $ is electric current flowing through the circuit
So, using this formula we can calculate power in series and parallel circuits.

Note :
The expressions for series and parallel resistance are derived from the laws of energy and charge conservation, which state that total charge and total energy are constant in any process. These two laws are directly involved in all electrical phenomena and will be invoked on numerous occasions to explain both specific effects and the general behavior of electricity.