How can you calculate base voltage of a transistor when there are biasing resistor and a resistor between 2 input terminal
You must analize the Thevenin's equivalent circuit:



where

$$
R_{th} = \dfrac{R_1\cdot R_2}{R_1 + R_2}
$$

and

$$
V_{th} = \dfrac{V_{CC}}{R_1+R_2}\cdot R_2
$$

then, the equivalent circuit



where \$V_b\$ is \$V_{th}\$ and \$R_b\$ is \$R_{th}\$

Then, you can write KVL, for the input circuit:

$$
V_b = i_b\cdot R_b + V_{BE} + i_b\cdot (\beta + 1) \cdot R_E
$$