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.