Please help will give lots of points and mark brainless

4, his answer was way off... idk if this is right but I tried

Step-by-step explanation:

s= √21d

42=√21d

42/21=√d

2=√d

4=d

in problems involving proportions, we can use cross products to test whether two ratios are equal and form a proportion. to find the cross products of a proportion, we multiply the outer terms, called the extremes, and the middle terms, called the means.

hope it