my right question is this.

Solve what???....we're just taking the cosine inverse to find  an angle whose cosine is = to the expression in the parentheses......

OK....that's a horse of a different color.....!!!

So we have

cos^-1 (((3*sqrt(3)+4) /(5*sqrt(10)))   =  54.43573387782 degrees

And there you go.....!!!

thank you very much CPHILL. and how to you solve it?