The following sum $$\frac{1}{1+\frac{3}{n}} \cdot \frac{3}{n} + \frac{1}{1+\frac{6}{n}} \cdot \frac{3}{n} + \frac{1}{1+\frac{9}{n}} \cdot \frac{3}{n} + \ldots + \frac{1}{1+\frac{3 n}{n}} \cdot \frac{3}{n}$$
is a right Riemann sum for a certain definite integral $$\int_1^b f(x)\, dx$$
using a partition of the interval $[1,b]$ into $n$ subintervals of equal length.

Then the upper limit of integration must be: $b$ =
and the integrand must be the function $f(x)$ =