The voltage gain Av of the circuit shown below is

Applying KVL in input loop,
13.7 – (I_C + I_B) 12k – 100k(I_B) – 0.7 = 0
⇒ I_B = 9.9μA ; I_C = βI_B = 0.99 mA ; I_E = 1 mA

∴ r_e =	26 mA	= 2.6 Ω ; z_i = βr_e = 2.6 kΩ ;
	I_E

∴ A_v =	(100 k \|\| 12 k)	= 412
	26

z_i' = z_i \|\|		100 k		= 221 Ω
		1 + 412

A_vs = A_v	z_i'
	z_i' + R_s

= (412)		221
		221 + 10k

| A_vs | ≈ 10