Please help asap with finding sum of arithmetic sequences

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

State if the two triangles are congruent. if they are, state how you know?

Which of the following is not a subset of {1,2,3}?