The second one would prove they are parallel. This is because it uses angles touching both of the parallel lines and uses correct Angle Properties
You would use the Pythagorean Theorem (a²+b²=c²)
7²+15²=c²
49+225=c²
274=c²
√274=c
or, 16.55=c
Add 4 to each side and the divide each side by 2.
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