In the figure shown here, what is the equivalent focal length of the combination of lenses (Assume that all layers are thin)?

The system consists of two plano-concave liquid lenses of refractive index \( n_2 = 1.6 \) and a biconvex lens of refractive index \( n_1 = 1.5 \) with \( R_1 = R_2 = 20\text{ cm} \). Using lens maker's formula for each part and combining powers gives \( F = -40\text{ cm} \).