The problem is finding the number of different solutions of the equation
r + y + g + p + b = 50
where r is the number of red balls, etc, subject to the constraints that:
r,\,y,\,g,\,p,\ \text{and}\ b \in \mathbb{Z}^+
r,\,y,\,g,\,p,\ \text{and}\ b \ge 4
r,\,y,\,g,\,p,\ \text{and}\ b <...