Once you have validated the idea, next step is to turn it into a business ( AKA Startup ).

Here is the formula to calculate the economics

A = Number of people with the same problem

B = Amount that each A is going to pay

C = A * B

D = Cost of providing B to A

If C>D, then there is a business. If not, there is not.

Now C wont be greater than D at all times, but in the long term, it should be.

Disclaimer : This is a very basic formula and is to calculate viability within minutes before deep diving into the detailed business modeling.