How can an amendment to the constitution be formally proposed

Through a joint resolution passed by two thirds vote or be a convention

Hope this helps!!

what is the tax base for the sales tax?

it should be (usually ) 6%

classical republicanism, also known as civic humanism, is a form of republicanism  developed in the renaissance inspired by the governmental forms and writings of  classical  antiquity, especially such  classical  writers as aristotle, polybius, and cicero.