Step 1: Picture the situation.
A asked B to build a cold storage for 50 lakh in 6 months. B failed. A quickly hired C to finish the work at 60 lakh and now wants the extra 10 lakh back from B. We must find the correct legal position under the Specific Relief Act, 1963.
Step 2: Identify the right idea.
When one party gets the work done by someone else and then claims the extra cost from the defaulter, this is called substituted performance. It was added to the Act by the 2018 amendment as Section 20.
Step 3: Learn the key condition.
Section 20 says that before getting the work done through a third party, the affected party must first give a written notice to the defaulting party. This notice must give the defaulter at least 30 days to perform. Only after this notice can the extra cost be claimed.
Step 4: Apply it to A.
Here A did not send any such written notice to B. A straight away hired C and then asked for the 10 lakh difference. Because the mandatory notice step was skipped, A loses the statutory right to recover that extra cost from B.
Step 5: Rule out the other options.
A can recover simply because B breached (option 3) is wrong, since the law still demands the prior notice. Saying A must sue only for damages and never for substituted performance (option 1) is too strict and not the real bar here. Needing the court to first declare B guilty (option 4) is not a requirement of Section 20.
Step 6: State the answer.
The real reason A cannot get the 10 lakh is the missing prior notice required by the Act. \[ \boxed{\text{A cannot recover the cost because A did not give B prior notice.}} \]