For each month of a given year except December, a worker earned the same monthly salary and donated one-tenth of that salary to charity. In December, the worker earned N times his usual monthly salary and donated one-fifth of his earnings to charity. If the worker's charitable contributions totaled one-seventh of his earnings for the entire year, what is the value of N? Select the correct option:
A) 31/4
B) 33/4
C) 29/4
D) 27/4
E) 25/4
Let monthly salary for each of the 11 months except December was x, then   11x*1/10 + Nx*1/5 = 1/7(11x + Nx);   11/10 + N/5 = 1/7(11 + N)   11+2N/10 = 11+N/7 =&gt;77+14N = 110+10N =&gt;4N=33   N = 33/4   Answer: 33/4
<result>B</result>
For each month of a given year except December, a worker earned the same monthly salary and donated one-tenth of that salary to charity. In December, the worker earned N times his usual monthly salary and donated one-fifth of his earnings to charity. If the worker's charitable contributions totaled one-seventh of his earnings for the entire year, what is the value of N?