Need Mobile Conversion Application

Need to develop a SIMPLE AND EASY stand-alone conversion app for IOS and Android that will compute some values from received input. There are multiple input fields with rolling and scrolling input fields/checkboxes. The mathematics/calculations required from the developer will be very basic adding, subtracting, division and multiplication. (These will be changed by the employer with protected calculations) Back-end code will be mostly repetitive IF-ELSE statements. No website, saving, database or Back-end architecture required. One main screen with dynamic text and options depending on conversion selected. You must be able to update text dynamically, check-uncheck checkboxes, do onclick, onchange kind of operations. You must be able to do screen layout compatible with different devices and with professional looking input fields and buttons. (Final image to be provided) See attached image of basic layout. Please advise in your bid which development language and IDE you will use as employer will expand app with protected content. Milestones will be created for: 1. Graphics delivery with "About" and "Help" 2. Dynamic input of all fields and buttons and Calculation to result 3. Final delivery with validation of input, warnings Detailed information will be given to winning bidder, but the app is really simple, just layout is a bit complex.