what ever you do not try to mow across a slope like that. the maximum safe angle when traveling across a slope on a ride on or tractor is around 20 degrees and thats recommended by the manufactures. this is especially applicable for ride ons because they have a very narrow wheel base considering all the weight and center of gravity is over 1/2 way up their frame. many have tipped and roled and the results are not pretty considering its 100 odd kg laying on top of you! this happened to my neighbor in his dried up [Censored] and he was hospitalized for 3 months with neck injures.
you'd want good brakes too!
chris, what type of mower do you have?
regards jay