The radius of a circle is 3.8 feet find the diameter

What is the best way to answer questions with a x expression in the question. for example 3x + 10x=?

If mary had 320 toy cars and she gave her friend 50 cars and then she gave her brother 72 more cars how much toy cars would mary have left ● explain with proper details

The candy store is having a 30% off sale. emma is going to buy $7.50 worth of candy.how much will she pay after the discount