Answer
$1.65~diopters$
Work Step by Step
We can find the required refractive power as follows:
$P=\frac{1}{f_1}+\frac{1}{f_2}$
$\implies P=P_1+P_2$
We plug in the known values to obtain:
$P=4.00~diopters+(-2.35)~diopters$
$\implies P=1.65~diopters$
