Given information:
- Radius of curvature of curved face in the plano-convex and plano-concave lens = 15 cm each
- Refractive index of the material of the lenses = 1.5
- Distance between the lenses = 20 cm

Calculating the focal length:
The focal length of a lens is given by the formula:

1/f = (μ - 1) * (1/R1 - 1/R2)

where f is the focal length, μ is the refractive index of the lens material, R1 is the radius of curvature of the first surface, and R2 is the radius of curvature of the second surface.

For the plano-convex lens:
- R1 = ∞ (since one surface is flat)
- R2 = 15 cm

Substituting the values into the formula:

1/f_pc = (1.5 - 1) * (1/∞ - 1/15)
= 0.5 * (0 - 1/15)
= -1/30

Therefore, the focal length of the plano-convex lens is -30 cm.

For the plano-concave lens:
- R1 = 15 cm
- R2 = ∞ (since one surface is flat)

Substituting the values into the formula:

1/f_pcc = (1.5 - 1) * (1/15 - 1/∞)
= 0.5 * (1/15 - 0)
= 1/30

Therefore, the focal length of the plano-concave lens is 30 cm.

Calculating the position of the image:
To calculate the position of the final image formed, we can use the lens formula:

1/f = 1/v - 1/u

where f is the focal length, v is the image distance from the lens, and u is the object distance from the lens.

For the plano-convex lens:
- Object distance (u_pc) = -20 cm (since the object is on the left side of the lens)
- Focal length (f_pc) = -30 cm (negative because the lens is diverging)

Substituting the values into the lens formula:

1/-30 = 1/v_pc - 1/-20
-1/30 = 1/v_pc + 1/20

Simplifying the equation, we get:

1/v_pc = -1/30 - 1/20
= -2/60 - 3/60
= -5/60
= -1/12

Therefore, the image distance for the plano-convex lens is -12 cm.

For the plano-concave lens:
- Object distance (u_pcc) = -12 cm (since the object is on the left side of the lens)
- Focal length (f_pcc) = 30 cm

Substituting the values into the lens formula:

1/30 = 1/v_pcc - 1/-12
1/30 = 1/v_pcc + 1/12

Simplifying the equation, we get:

1/v_pcc = 1/30 - 1/12
= 1/60

Therefore, the image distance for the plano-concave