Make Free Shipping The ONLY Option

I have set up a Free Shipping option on any order over $75. The problem is when someone places an order over $75 it shows TWO options: the normal Flat Rate of $5.00 (which is clicked by default) and the Free Shipping. They have to choose one of the two options. Many of the customers don’t notice this and just leave the Flat Rate clicked and so they don’t get the free shipping they are entitled to. Is there a way to remove the Flat Rate option from these orders so that the Free Shipping is the only option on any order over $75? Thank you for any help or guidance.

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