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Solve Riddles

First to solve, for $1.87 $1.88 $1.89 $1.91 $1.94 $1.99 $2.07 $2.20 $2.41 $2.75 $3.30 $4.19 $5.63 $7.96 $11.73 $15.50 $21.60 $31.47:

x=1 y=1 z=2
x=1 y=2 z=2.5
x=2 y=1 z=2.5
./z=...