we know that
ρ = density of gasoline = 737 kg/m³ (at T = 60°F = 15.6°C)
ρ = m/V
ρV = m
V = m/ρ
V = 49.0 kg / 737 kg/m³
V = 0.066 m³
[volume of the tank]=L*W*H-----> H=volume/[L*W]----> H=0.066/(0.9*0.4)
H=0.1833 m
the answer is
the depth of the tank is 0.18 m