How can I assign calculation values and use them in a calculation?

I want to create a form with a calculation field that does the following:

If Numeric Field A = 1 - 20

Field B = Field A x $10

or 

If Numeric Field A = 21 - 50

Field B = Field A X $15

Is there a way to make these calculations happen without writing 50 separate conditional formulas for each number?

(i.e. if Field A equals 1, if Field A equals 2, if field A equals 3... etc)

You won't need to create 50 conditions for this. The key feature you're missing here is the ability to assign Calculation Values for each option (e.g. Options 1 to 20 on a Dropdown menu can have a respective calculation value).

Complete guide: How-to-Assign-Calculation-Value

After assigning a value for each, use those values for your calculation.

Related guide: How-to-Perform-Form-Calculation-Using-a-Widget

Example: https://www.jotform.com/72891162443963

You can clone the form above if you wish to have a closer look. But basically, the form was created based on the principles outlined on the 2 guides mentioned above.