Answer:
Speed of boat in still water is 6km/h
Speed of current is 4km/h
Step-by-step explanation:
We know speed = distance / time
Let the speed of boat in still water be x
Let the speed of current be y
Hence the speed of boat, down stream = 
Distance downstream = 20km
Time taken = 2 hours
We have

......(1)
Speed of boat upstream = 
Distance upstream = 4
Time taken = 2
We have

...(2)
Adding (1) & (2)


Substituting in (1) we get

The z-score of the data can be calculated by the formula expressed as follows:
z = ( score - mean ) / standard deviation
z = (126 - 150 ) / 11 = <span>-2.18
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A z-Score<span> is a statistical </span>measurement<span> of a </span>score's<span> relationship to the mean in a group of </span>scores<span>. A </span>Z-score<span> of 0 means the </span>score<span> is the same as the mean.</span><span>
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it would be 35/3 or 11 2/3