Step 1: Identify the breach. A and B agreed on a price of \( 50 \) lakh for B to construct the cold storage within six months. B did not complete the work in that period, which is a breach of the contract by B.
Step 2: Identify the substituted arrangement and its cost. After the breach, A engaged C to finish the same construction, and C's price was \( 60 \) lakh. This is the cost A actually had to pay to get the contract's object fulfilled once B defaulted.
Step 3: Compute the extra amount A is out of pocket. \[ \text{Extra cost} = 60 \text{ lakh} - 50 \text{ lakh} = 10 \text{ lakh} \] This \( 10 \) lakh difference exists only because B failed to perform; had B completed the work as agreed, A would never have needed to pay this extra amount.
Step 4: Apply the remedy of substituted performance. The Specific Relief Act, as amended, lets a promisee who has been met with a breach get the work substituted through a third party and then recover the extra expenditure from the defaulting party, without first needing a separate declaration of breach or being restricted to a bare damages claim. Applying this to the figures above: \[ \boxed{A \text{ can recover } 10 \text{ lakh from } B} \]