Let a_n be the n-th digit after the decimal point in 7π+7e. Evaluate

Let x be the number of tree planted. With this representation, the number of bushes planted is 3x. The equation that would best represent the situation above is,
                                        (x)(75) + (3x)(20) = 810
The value of x is 6. The number of bushes planted is 18. Thus, the answer is letter C.18.