How convince my mum to get me a dog if i already have a cat?!?

i asked her yesterday n she was up for iht until mi auntie unconvinced hur. she said tht we live in a flat n your not aloud dogs but theirs already pepo with dogs so :-S and the usuall excuse ALOT OF RESPONSIBILITY!!! she also said tht mi cat is 5 n she said tht she wood be scared but she wood get use to iht and then mi mum said tht she woodnt like a cat and dog in the same house and she said tht im is skewl all day and tht woodnt be fair on the dog but i cood take the dog out for a long time at 7 with mi friend who has a dog n she leaves iht in the house til she comes bk from skewl n thts fine!! plz help meh!!