Is Trevor the name of the toad?
ΔV = rise in volume of water, assuming the toad is fully submerged in the water, a fact that is not stated in the problem, but necessary to answer the question
ΔV = 2.50 L
m = mass of toad = 13.6 kg [That is an EXTREMELY massive toad!]
ρ = m/ΔV = (13.6 kg)/(2.50 L) = 5.44 kg/L