Relevant Contribution to sales ratios (%) – for productsWYZ Q 18/in Rev Kit 2014

Hello Sir,

Can you please answer me, how they did calculate the Contribution to sales Ratios in%?

Question 18 in BPP Rev Kit exams up to June 2014.
It is in part B) For each of the three products (W,Y,Z), calculate the relevant contribution per $ of material B for the next quarter.

Product W Y Z
SP $10 $15 $30
Relevant contribution 0.80 (2.10) 3.60
Contribution to sales ratios (%)
8% (14%) 12%
SIr , can you tell me how they got 8%, (14%), 12%??

Thank you in advance.