4a + 5b = 16.5 ........................(1)
2a + 3b = 9.5 ...............(2)
(1) X 10 = 40a +50b = 165 ......(3)
(2) X 20 =40a + 60b = 195 ...(4)
(4) - (3) : 10b = 25
b= 2.5 (cost of one pen)
from (2) and substituting b for 2.5 :
2a + (3x2.5) =9.5
2a= 9.5-7.5
a =2 (cost of one pencil)