I need a help for statistics ASAP!!

Three sets of researchers set out to examine the same research question: Do dog owners spend more money on their pet than cat owners, on average? To answer this question, the first set of researchers surveyed 20 cat owners and 20 dog owners about how much money they spend (annually) on their pet. The second set of researchers asked the exact same question, but sampled 40 cat owners and 40 dog owners. The third set of researchers again asked the exact same question, but sampled 70 cat owners and 70 dog owners. All three sets of researchers found that dog owners spent $1,641 each year, on average, and cat owners spent $1,125 each year, on average.

Compute the result from the observed data that all three sets of researchers will use to evaluate the model from their null hypothesis. Be sure you are computing this so it is consistent with your stated hypothesis (The null hypothesis would be that there is no difference in the amount of money spent for the pet by dog owners compared to the money spent for the pet by cat owners. )