How do I solve this problem

Cost of 7 gallons=$24.50

Cost of 1 gallon=24.50/7=3.5

Cost of 15 gallons=15*3.5=52.5

Cost of 15 gallons will be $52.5

y=2x+15

where y=Value of coin

x=Age in years

Value of coin after 19 years=2*19+15

=$53

Therefore, Value after 19 years=$53

The answer is in the image 

Speed=Distance/time

Here,

distance=15m

time=1sec

speed=15/1=15m/sec

Distance=Speed*time

time=15min=15*60sec=900sec

Distance travelled in 15 min=15*900=13,500m

=13500/1000 km=13.5Km

The wood before starting =12 feet

Left wood=6 feet

Wood used till now=12-6=6 feet

Picture frame built till now= 6/(3/4)

=8 pieces

Therefore, till now 8 pieces have been made.

The answer is in the image 

We can put the numbers in ascending order-

36, 38, 39, 39, 40, 47, 48, 51

Range=max-min

          =51-36

          =15

III is the case of joint variation as Area A depends on l and w

In I and II it depends on s and r respectively as pi is constant

Given,

Area of base = 6ft

Volume = 15ft

We know,

Volume = area of base * height

15 = 6 * height   

height = 15/6

   = 2.5ft   

Volume of rectangular prism = length * breadth * height

Given,

Length = 6 cm

height = 1 cm

Width = 4 cm

Volume = 6 * 1 * 4

=24 cm^3