So we need to recall 2 basic formulaes for deadlock and no deadlock
R is resources ,n is number of processes and Si is resource copy alloted for each process.
- If deadlock present R<=$\sum_{i=0}^{n}Si-n$
- If no deadlock R>$\sum_{i=0}^{n}Si-n$
now question demands for no deadlock so R>(12+9+20)-13
R>28 so min value for no deadlock is 29