Ihave trouble finding the nth term of a linear sequence

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

Solve the equation: x - 9 = -6 + 5 a. 21 b. 7 c. 14 d. 2

240 seventh graders and two-thirds of the students participate in after-school activities how many students participate in after-school activities