The cost of 18 pens and 4 pencils is ₹200. If the cost of a pen decreases by Rs. 1 and the cost of a pencil increases by Rs. 3, then the cost of 19 pens and 3 pencils is Rs. 151. What is the original cost of 12 pens and 10 pencils?

Correct option is B

Solution:

Let original cost of a pen = ₹p, pencil = ₹q

18p + 4q = 200

After change: pen → p - 1, pencil → q + 3

19(p-1) + 3(q+3) = 151

19p + 3q = 161

Multiply (1) by 3 and (2) by 4:
54p + 12q = 600
76p + 12q = 644
Subtract:
22p = 44 

p = 2
Plug into 19p+3q=161:
38 + 3q = 161

3q = 123

q = 41
Original cost of 12 pens and 10 pencils:
12p + 10q = 12(2) + 10(41) = 24 + 410 = ₹434