Part a: For variable X using z score you have (x-30)/10, replace X for this expression in (a), i mean Z=2+10((x-30)/10) = 2+x-30= put this in the way of z score = (x-18)/1, so the mean is 18 and standard deviation is 1.
Part b: Z=X+Y= (x-30)/10 + (x-20)/8 = solve adding fractions = (18x-440)/80 now divide all the numbers between 18 (because you need to show as z score way) = (x-24.4)/4.4, so the mean is 24.4 and standard deviation is 4.4.
For part c,do the same.
Zoe's unit rate is 0.625
Explanation
Just divide because remember unit rates are out of 1.
Sinx=1/2
sin30=1/2
therefore x=30 degree
While writing inequalities we should know about symbols
a>b means a is greater than b
a<b means a is less than b
so here we have to write
difference between t and 7= t-7
given t-7 is greater than 10 so t-7>10
and t-7 is less than 20 so t-7<20
combining above two we get
10<t-7<20, <span>17 < t < 27</span>
It would be 20 hrs because if you put them both in an equation aka y=25x+100 and y=30x just plug in numbers into the x until they both have the answer which in this case is 20