Solved it by using the scale method (scale should be always of the same variable, here it is protein).

Protein in X ----- Avg Protein after mixing --------- Protein in Y

Based on above the scale becomes as below:

(Soln X) 10-----

<\(\frac{38}{3}\)-10>-------\(\frac{38}{3}\)----

<15-\(\frac{38}{3}\)>------

15 (Soln Y)\(\frac{X}{Y}\)=(15-\(\frac{38}{3}\))/(\(\frac{38}{3}\)-10)=\(\frac{7}{8}\)

To know X from the total mixture/solution= \(\frac{X}{X+Y}\)=\(\frac{7}{(7+8)}\)*300=\(\frac{7}{15}\)*300=140

Answer=(B)

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Non-Allergic To Kudos