Sally needs 50% to pass. If she gets 480 marks and fails by 20 marks. What were the max marks she could have?

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

3382-299=3383- ? fill in the blank?

We just started the introduction into circles and i have no idea how to do this.