We’re being asked to determine the normal boiling point of ammonia. We’re given the vapor pressure at different temperatures. 

For this problem, we can use the Clausius-Clapeyron Equation:

$\boxed{\mathbf{ln}\frac{{\mathbf{P}}_{\mathbf{2}}}{{\mathbf{P}}_{\mathbf{1}}}\mathbf{=}\mathbf{-}\frac{{\mathbf{\Delta H}}_{\mathbf{vap}}}{\mathbf{R}}\left[\frac{\mathbf{1}}{{\mathbf{T}}_{\mathbf{2}}}\mathbf{-}\frac{\mathbf{1}}{{\mathbf{T}}_{\mathbf{1}}}\right]}$

where:

P₁ = vapor pressure at T₁

P₂ = vapor pressure at T₂

ΔH_vap = heat of vaporization (in J/mol)

R = gas constant (8.314 J/mol•K)

T₁ and T₂ = temperature (in K).