SuiteApp Version: eXtendMobile 1.10 and above
Mobile App Version: 1.10 and above
Audience: Administrator

Use Case:
You want to create a function where the amount is calculated automatically based on the rate and quantity specified on transaction line items.

Resolution:
You can use Dynamic Formula Fields to perform this behavior. Refer to 
Dynamic Formula Fields for details on creating a dynamic formula that will automatically calculate the amount.