if 8 pens and 7 pencils cost $3.37 while 5 pens and 11 pencils cost $3.10, how much does each pen and pencil cost?

Let a=number of pens and b=number of pencils.
8a+7b=3.37; 5a+11b=3.10.
To eliminate a variable multiply the first eqn by 5 and the second by 8:
40a+35b=16.85, 40a+88b=24.80.
Subtract these equations: 53b=7.95, b=$0.15. So 5a=3.10-1.65=$1.45, a=$0.29.
Pens are $0.29 each and pencils $0.15.