14000+7x=35x (x being the number of books) solve for x and you have your answer. 14000=35x-7x=28x therefore x=14000/28=500 so he needs to sell 500 books before he breaks even.
Answer: The answer is d. 64 units
The answer for the first one is city c
Suppose:
C=cost
c=cost per kilo-watt hour
w=number of watts
h=number of hours
thus
C=kwhc
where:
k=constant of proportionality:
k=C/(whc)
but
C=15 when w=6000, h=10/60=1/6 hours, c=7.5 cents per kw/h
thus
k=15/(6000*1/6*7.5)
k=0.002
thus:
C=0.002(whc)
hence:
when
h=70*2=140=140/6=70/3 hours the cost will be:
C=0.002(6000*70/3*7.5)
C=2100 cents
C=$21
