Conditional Display of Form Fields

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Hi folks! I'm wondering if there's an add-on available that lets me create one form for several closely-related purposes. Most of the fields for the forms are the same, so they would display on all forms. However, some of the fields relate to only one form, so I'd like to display that field only when another field is selected. For example:

1. Name, address and phone number displays on all forms.

2. A field called "Type of Request" uses radio buttons and has these options: Request A, Request B, Request C.

If the person selects the "Request A" radio button, these additional fields are displayed: Textarea 1, Checkbox 1

However, if the person selects "Request B" radio button, these additional fields are displayed: Textarea 2, Checkbox 2

Is there an add-on that does this? If not, is it possible to *easily* code this somehow? (I'm not a css/php/js wizard so it would have to be fairly straightforward.)

Thanks for any help provided!

Chris