Hey there!
We can set up an equation. Since 20% is said as twenty percent, we can conclude that it says "per-cent", which means "per hundred", like century is a hundred years. That way, we can say that 20% is also written as a decimal of twenty hundredths, because it's per hundred. Thus, we're saying that his down payment, 1,600, is (this is keywording for equals) 20% of (keyword for multiplication) the total price (x). That gives us:
1,600 = .20x
Divide both sides by .20
x = 8,000
Therefore, the cost of the car was 8,000 dollars.
Hope this helps!