Manoj deposited 29400 Rs. for 6 years at a simple interest. He got 4200 Rs. as interest after 6 years. The annual rate of interest was :
[A] $2\frac{8}{21}\%$
[B] $2\frac{7}{20}\%$
[C] $3\frac{8}{21}\%$
[D] $4\frac{8}{21}\%$