Question

In 1990, when the consumer price index (CPI) was 130.7, Deena purchased a house for $98,700. Assuming that the price of houses increased at the same rate as the CPI from 1980 to 1990, approximately how much would the house have cost in 1980, when the CPI was 82.4?

Answer 1

so, it's just a matter of "ratios"
we could say that
$$\bf \large {
\cfrac{82.4}{130.7} = \cfrac{\color{red}{Price}}{98,700}
}
$$

now just solve for "price"