Answer:
or

Step-by-step explanation:
we know that
The scale of the drawing is equal to divide the length of a building in the scale drawing by the actual length of a building
so
That means
15 cm in the drawing represent 37.5 ft in the actual
Remember that

Convert 15 cm to ft
divide by 30.48

substitute

or

That means
1.31 units in the drawing represent 100 units in the actual
An=a1r^(n-1)
given
a5=1/24
a10=1/768
we know that
a5=1/24=a1r^(5-1) and
a10=1/768=a1r^(10-1)
so
1/24=a1r^4
1/768=a1r^9
(a1r^9)/(a1r^4)=r^5=(1/768)/(1/24)=1/32
r^5=1/32
take 5th root of both sides
r=1/2
we have
a5=a1r^4=1/24
evaluate r^4 or (1/2)^4
1/16
a1(1/16)=1/24
times both sides by 16/1
a1=16/24
a1=2/3
the first term is 2/3
9/10. make the bottom numbers the same to add fractions. you can do that by multiplying 7/10 by 10/10.
70/100 + 20/100 = 90/100
90/100 = 9/10
you can also reduce 20/100 to 2/10.
7/10 + 2/10 = 9/10