whovever answers first will get brainliest and if you delete my question i will ANNIHILATE you. thank you ^w^

Arandom high school question but a hard one

Asilkworm winds its cocoon out of one long silk fiber. to make silk thread, 3 to 10 of these silk fibers are unwound from their cocoons and combined into aa single thread with a typical length of 300 yards. choose a reasonable number of silk fibers in a thread write an equation to find the total length of the silk fibersused in 300 yards of the thread

Given the equation f(x)=a(b)x where the initial value is 40 and the growth rate is 20% what is f(4)