A contractor is going to cast a slab$-$on$-$grade for a large family house. To cast a $200$ mm thick and $500$ m$2$ large slab, she estimates that a total volume of $100$ m$3$ concrete is needed. However, the base underneath the slab is not completely even. Anticipate that the needed concrete volume is N$(100$; $5)$ m$3.$ The concrete will be delivered from a ready mix concrete plant by a number n of truck mixers. Assume that every truck mixer delivers a volume that can be assumed to be normal distributed expressed by N$(6$; $0,6)$ m$3.$ These volumes are considered to be independent from each other. Determine the smallest number n that leads to a sufficient total concrete volume with a failure probability limited to p $=0,05.$