(a) : We $1^{\text {st }}$ note that a number is dividible by 3 if the sum of the digits is divisible by 3 . Hence from the given digits the eligible candidates are $0,1,2,4,5$ or $1,2,3,4,5. \\$ Number of arrangements in $1^{\text {st }}=15-14$ and in $2^{\text {nd }}$ is 5. $\\$ ∴ Total number of desired numbers is $96+120=216$.