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Calculating the energy of a photon of a wavelength and work function

In my AQA Physics book I have a problem with a question relating to The Photoelectric Effect, It consists of two parts so I have posted both:

Light of wavelength 635nm is directed at a metal plate at zero potential. Electrons are emitted from the plate with a maximum kinetic energy of 1.5x10 -19 J

Calculate:

The energy of a photon of this wavelength

I tried to work this out with the formula:

E = hc / λ

E = (6.63x10 -34 * 3x10 8) / 635
= 3.13228x10-28

Is this correct, the answer seems low?

The next question asked to calculate the work function of the metal:

I used

E = hf - ϕ

E - hf = -ϕ

-E + hf = ϕ

hf - E = ϕ

This worked out to:

6.63x10 -34 * 472440.9449 - 1.5x10-19
= -1.499999997x10 -19

I don't see how this can be correct as it is negative.

The final question asks to calculate the threshold frequency of electromagnetic radiation incident on this metal

That should be the formula:

f = ϕ / h

f = -1.499999997x10 -19 / 6.63x10 -34

This is negative.

Is this the correct method for solving this?