How to solve both of this

GRE Quant Problem Solving
1

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                                     and

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2

Greg did a walk-through of the Big Bookhttps://www.gregmat.com/course/old-gre-walkthroughs

3

thanks

4

@HoldMyBeer first question is not covered by greg, so can you please explain

5

Hint: think about similar triangles, namely the shaded triangles with \Delta ABC.