Mr Okafor cannot see clearly any object that is nearer than 40 cm…

Step 1. The lens at the eye. $u = -25\ \text{cm}$ and $v = -40\ \text{cm}$. $\dfrac{1}{f} = \dfrac{1}{v} - \dfrac{1}{u} = -\dfrac{1}{0.40\ \text{m}} + \dfrac{1}{0.25\ \text{m}} = -2.5\ \text{D} + 4.0\ \text{D}$. So $P = +1.5\ \text{D}$.

Step 2. The spectacles. The lens is $2.0\ \text{cm}$ from the eye. So $u = -(25 - 2.0)\ \text{cm} = -23\ \text{cm}$ and $v = -(40 - 2.0)\ \text{cm} = -38\ \text{cm}$.

Step 3. The power. $\dfrac{1}{f} = -\dfrac{1}{0.38\ \text{m}} + \dfrac{1}{0.23\ \text{m}} = -2.632\ \text{D} + 4.348\ \text{D} = 1.716\ \text{D}$. So $P = +1.72\ \text{D}$.