elena purchased brand x pens for $ 5.00 apiece and brand y for $ 2.80 apiece. if elena purchased a total of 12 of these pens for $ 42.00, how many brand x pens did she purchase? Choose the correct option
A) 4
B) 5
C) 6
D) 7
E) 8
<gadget id="calculator">4 * 12</gadget>
<output>48</output>

<gadget id="calculator">48 - 42</gadget>
<output>6</output>

<result>C</result>
elena purchased brand x pens for $ 5.00 apiece and brand y for $ 2.80 apiece. if elena purchased a total of 12 of these pens for $ 42.00, how many brand x pens did she purchase?
subtract(multiply(const_4.0, 12), 42.00)
"4 x + 2.8 y = 42 - - > multiply by 2.5 ( to get the integers ) - - > 10 x + 7 y = 105 - - > only one positive integers solutions x = 6 and y = 5 ( how to solve : 7 y must have the last digit of 5 in order the last digit of the sum to be 5 ) . answer : c ."