Please tell whether the answer written below is correct after checking the question given in the picture ..
In many books I have seen that demand curve is shifted towards its left (because it is given in the question that they are complements) . But can we attempt the question in this way ? Why or why not?because it is not mentioned in the question whether supply curve should be shifted or demand should be shifted .. pl explain in detail

Dear student,

We should be using the demand curve in this case because Demand curve shows us how much of a consumers is willing to purchase(bought), at different price points. It correctly depicts the bought and sold side(as consumer is demanding it and it will be sold for sure.)
While a supply curve shows the amount of a product that a supplier is willing and able to offer to the market, at specific price points.It shows the supply side of the things.(We are not sure if whatever is supplied at a given price point is sold or not.)

Hope it helps.

Regards,