Answer:
a) 
b)
Step-by-step explanation:
We are given in the question:

F(x,y,z) = (y, -x, z)
a) 
We differentiate with respect to t.

b) F(c(t))
This is a composite function.


Answer:
-0.2?
Step-by-step explanation:
Just solve the equation.
That's a 33% increase.
I calculated this using the formula:

Where n = the new value (16 in your question), o = the old value (12 in your question) and the result is outputted as a percent increase. You can check that this is correct by finding 33% of 12, adding the result to 12, and checking that the result equals your "new" number.
Note that 33% is only an approximation as your question requires a number rounded to the nearest whole.
To solve for the coefficient of variation you will need this formula:
CV = (SD/X) x 100
Where: CV = Coefficient of Variance
X = Mean/average
SD = Standard Deviation
To determine which one is more variable, just get the coefficient of both and compare.
AGE SALARY
CV = (6/55) x 100 CV = (4,100/37,000) x 100
= 10.90 = 11.08
Based on the results, salary is more variable because 10.90<11.08.