So... hmmm if you check the first picture below, for 2)
we could use the proportions of those small, medium and large similar triangles like

now.. for 3) will be the second picture below
Answer:
d on edge
Step-by-step explanation:
-3(x+4)(x-2)/x^2-1`
Number of strings =

= 21 x 21 x 21 x 21 x 21 x 5 = 20 420 505
Answer: 20 420 505