Number Stairs

hi, has any one done the GCSE Number stairs coursework? i have got it to do, what i want to know is, does anyone know the formula for, any step on a 10by 10 grid, as i am completely stuck :(

i think u label one side on square and then label oter side then put

xy = k

x being horizontal
y being verticle
k being number wanting to find

but im probably wrong as i only done ks3 maths