Answer: A roll of plain wrapping paper costs $17, while a roll of holiday wrapping paper costs $20.
Step-by-step explanation: First let us represent a roll of plain wrapping paper with letter p and a roll of holiday wrapping paper would be represented by d. If Eduardo sold 5 rolls of plain wrapping paper and 5 rolls of holiday wrapping paper for $185, then we can express this as
5p+ 5d= 185
Also if Sarawong sold 14 rolls of plain wrapping paper and 5 rolls of holiday wrapping paper for $338, then this too can be expressed as
14p + 5d = 338
Now we have a pair of simultaneous equations which are,
5p + 5d = 185 ———(1)
14p + 5d = 338 ———(2)
Since all the variables have coefficients greater than 1, we shall use the elimination method. Note that the coefficients of the d variable are both 5, so straight away we subtract equation (1) from equation (2) and we now have;
(14p - 5p) + (5d - 5d) = 338 - 185
9p = 153
Divide both sides of the equation by 9
p = 17
Having calculated p, we can now substitute for the value of p into equation (1)
5p + 5d = 185
5(17) + 5d = 185
85 + 5d = 185
Subtract 85 from both sides of the equation
5d = 100
Divide both sides of the equation by 5
d = 20
Hence, the cost per roll of plain wrapping paper is $17, while the cost per roll of holiday wrapping paper is $20.