GATE CS Deadlock questions

Which of the following is not a valid deadlock prevention scheme?

A computer has six tape drives, with $n$ processes competing for them. Each process may need two drives. What is the maximum value of $n$ for the system to be deadlock free?

An operating system contains $3$ user processes each requiring $2$ units of resource $R$. The minimum number of units of $R$ such that no deadlocks will ever arise is

Consider a system having $m$ resources of the same type. These resources are shared by $3$ processes $A, B$, and $C$ which have peak demands of $3, 4$, and $6$ respectively. For what value of $m$ deadlock will not occur?

A computer system has $6$ tape devices, with n processes competing for them. Each process may need $3$ tape drives. The maximum value of n for which the system is guaranteed to be deadlock-free is: