Radial Electric Fields

The question is 'a Van de Graaff generator is charged with 2.5 x 10^-7 coulombs in a school lab demonstration. The spherical metal dome has a diameter of 30cm.

a) what is the electric field strength at a distance of 5cm from the surface of the charged dome?
b) what is the electric potential at a distance of 35cm from the surface of the charged dome?

I know that the answers are a) 56000 vm^-1 and b) 4500V but I don't understand how to get there!! Please help xx

The metallic dome of the Van de Graaff generator can be considered as uniformly charged spherical shell. For the electric field, draw a Gaussian sphere of radius 20cm (30 cm diameter so 15 cm radius and add 5 cm to get 20 cm). And then use the famous equation for electric field. KQ/r^2 to get the electric field equal to 56,250 V/m.

For electric potential use K Q/r with r = 50 cm to get 4500 V.

Hope this helps.