the results of a survey of 100 households pointed to shoppers having a preference for house brand products in supermarkets It showed that of 280 households with a combined income of $6000 per month, 71 reported buying house brand products from June to December This is compared to 60 during the preceding 6 months - an increase of x%.

Question

the results of a survey of 100 households pointed to shoppers having a preference for house brand products in supermarkets  It showed that of 280 households with a combined income of $6000 per month, 71 reported buying house brand products from June to December  This is compared to 60 during the preceding 6 months - an increase of x%.
Supermarket, Lo-Cost, Cooking Oil, House brand $5.46 (2qt), Commercial Brand $8.10 (2qt)
Kelly's, Bread, $1.60, House brand $1.6 (1lb), Commercial Brand $1.85(lb)
a) calculate the value of x
b) find the values of y and z
  (i) The commercial brand cooking oil cost y% more than house brand one
  (ii)The commercial brand bread cost z% more than the house brand one.