To get the answer for this particular problem you would do the following:
Multiply the original price (771) by the percentage that is being added. REMEMBER! Since it's a percentage, you have to turn it into a decimal by moving the decimal over two places. So, 20% would become .20. And you always multiply by the DECIMAL you just made and NOT the actual percentage.
Multiplying these two, you would get 154.20. This is the amount that is being added to the original price, so you'd have to add $154.20 to the original price of $771.
You get your answer! $771 + $154.20 gives you $925.20. So, your end price is $925.20.
And, if you were asking for how much the increase would be, then it would increase by $154.20, as said in step two.