Answer:
2.17
Explanation:
As the population variance is known we can calculate population standard deviation and so, z-test statistic will be used.

population variance=σ²=0.36
population standard deviation=σ=√0.36=0.6
The value of population mean can be achieved through null hypothesis.
Null hypothesis : μ=7.4
Alternative hypothesis : μ≠7.4
population mean=μ=7.4
xbar=7.5
n=170
z=(7.5-7.4)/(0.6/√170)
z=0.1/(0.6/13.038)
z=0.1/0.046
z=2.17
Thus, the calculated z-test statistic is 2.17.