I am running a e com store and just created the website. Now my business is growing and i want to make mobile app of best japanese vegetable knives (https://toolsofchef.com/best-japanese-vegetable-knives/) my store. Is there a developer here who can tell me how much it would cost to build a mobile app?

getting below error i am stuck someoe help pls

Challenge Not yet complete... here's what's wrong: 
There was an unexpected error in your org which is preventing this assessment check from completing: System.DmlException: Insert failed. First exception on row 0; first error: CANNOT_EXECUTE_FLOW_TRIGGER, We can't save this record because the “Launch Shift Approver” process failed. Give your Salesforce admin these details. An unhandled fault has occurred in this flow
An unhandled fault has occurred while processing the flow. Please contact your system administrator for more information. Error ID: 1520688709-82059 (804213384): []

Learning Salesforce DX, have downloaded the DreamHouse project from gitHub site, made a new branch of my own.  Then, in the Unit of "Create and Test Our Scratch Org", at the beginning, it says "Enter cat config/project-scratch-def.json" to see some of the options available. When I did this in the command line, I got "cat not recognized as an internal or external command".  Online articles say that "cat" is a Unix code, can't be used in Windows system.  Now, my question is what should I use in Windows?

Thanks!