Two discrete random variables have a uniform joint PMF given by PM.N(m, n) = c, for 0 20)

Two discrete random variables have a uniform joint PMF given by for 10,091 < 25. Outside this region, the PMF iS zero. (a) Find the value ot the constant c_ (b) Find Pr(M + N < 10) - (C) Find Pr(M + N > 20).