Find the missing side length in the image below

? = 5

Step-by-step explanation:

Recall: when 2 transversal lines cuts across 3 parallel lines, the parallel lines are divided proportionally by the transversals.

Therefore:

?/10 = 3/6

Cross multiply

?*6 = 3*10

?*6 = 30

Divide both sides by 6

? = 30/6

? = 5

b) well because you get well