Item.
Solutions where \(x_1 > 3\text{:}\) \({13 \choose 4}\text{.}\) Give \(x_1\) 4 units first, then distribute the remaining 9 units to the 5 variables.
Solutions where \(x_1 > 3\text{:}\) \({13 \choose 4}\text{.}\) Give \(x_1\) 4 units first, then distribute the remaining 9 units to the 5 variables.