How do I solve 4x+y=0 and 5x-y=9

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

Find the value. a. 0.003 b. 0.03 c. 0.3 d. 3

Which statement justifies why angle ebc measures 90?