A: A number of books and their cost using the subscription that charges per book B: A number of books and their cost using the subscription with the annual fee

C: A number of books and their cost where both subscriptions cost the same

D: A number of books and their cost that is not possible with either subscription

a

step-by-step explanation:

we have three similar triangles, because each has a right angle and shares an angle.   let's write the angles in order: opposite to short leg, long leg, hypotenuse.

cab similar to bad similar to cbd

or as ratios,

ca: ab: cb = ba: ad: bd = cb: bd: cd

we also know

ac = ad + cd

(ad+cd): ab: cb = ba: ad: bd = cb: bd: cd

(ad+cd)/cb=cb/cd

we have cb=6, ad=5 and seek x=cd.

we reject the negative root and conclude x=4

answer: 4

answer:

a=9

step-by-step explanation: lmk if you need a explanation