Answer:
See below.
Step-by-step explanation:
[tex] z = \dfrac{15 - 12}{\frac{2.8}{\sqrt{20}}} [/tex]
[tex] z = \dfrac{3}{\frac{2.8}{\sqrt{4 \times 5}}} [/tex]
[tex] z = \dfrac{3}{\frac{2.8}{2\sqrt{5}}} [/tex]
[tex] z = 3 \times \dfrac{2\sqrt{5}}{2.8} [/tex]
[tex] z = \dfrac{6 \sqrt{5}}{2.8} [/tex]
[tex] z = \dfrac{13.416}{2.8} [/tex]
[tex] z = 4.792 [/tex]
