I don't think there's an easy answer to 3^x=5x, but trial and error. Put x=1, 2 and 3 into the function 3^x-5x and we get -2, -1 and +12. These trials tell us the answer is between 2 and 3 because the sign goes from - to +. So using a calculator we put x=2, 2.1, 2.2, etc. and keep an eye on the sign changes. When you see the sign change between 2.1 and 2.2, you're ready to move to the next decimal place, and so on. When I did this I got 2.1703. You can also use Newton's method (calculus).