The total cost of 45 pens and 24 pencil is Rs.
675. What is the total price of 8 pens and 15
pencils

actually we should have 2 equations to solve two parameters. But i am solving like this.
let take pens = X and Pencils =Y
45X+24Y=675
This we can write 15X+8Y=225
Here by trail and error method we only getting one solution X=7 and Y=15.
They asked 8X+15Y = 8*7 + 15*15 = 281. Please tell me its correct or not.

Could be consistent or inconsistent , second equation is required to check consistency.