Let the number of bundles formed by pens be x;
let the number of bundles formed by pencil be y.
acc. to 1st condition;
acc.to the 2nd condition;
multiplying (ii) by 8;
adding (i) and (iii);
therefore x=15-y=15-6=9(from eqn (ii));
total no. of pens=8x=8*9=72 pens.