Two free vortices of equal strength, but opposite direction of rotation, are superimposed with a uniform flow (v~ = uˆi). the first vortex, of clock-wise rotation, is located at (0,h) and the second is located at (0,-h). the stream function for a vortex of positive strength is given by

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.

you'd use the equation that establishes a relationship between  energy  and  wavelength, which looks like this

e=h⋅cλ, where

λ  - the wavelength of the photon; c  - the speed of light, usually given as  3⋅108m/s; h  -  planck's constant, equal to  6.626⋅10−34j s

plug the value you were given for the energy of the photon in the above equation to get the wavelength

e=h⋅cλ⇒λ=h⋅ce

λ=6.626⋅10−34js⋅3⋅108ms−1.257⋅10−24j=1.581⋅10−1m