Economics Help: Taxes paid on the first $30,000 are taxed at a %20 rate, while taxes paid on all income above?

Question

$30,000 are taxed at a 10% rate. If you earn a $100,00 in income:

A. What is your average tax rate? ______
B. What is your marginal tax rate?______

Please show me how you got this cuz im sooo confused : )

Answer 1

total tax = .20*30000+.10(100000-30000)=6000+7000=13000
average tax =13000/100000=.13 or 13%
marginal tax =10% or tax on additional dollar earned