How to solve these? I would like explanation please

Step-by-step explanation:

9.

it is a rectangle. 18m × 4m = 72 m²

the paving costs $35 per m², and we have 72 m², so it does not take a genius to figure out what to do next ...

right : we multiply 35 by 72

35×72 = $2520

10.

how much volume is a liter ?

a liter fits into a cube of 10cm side length.

and 1 meter = 100 cm = 10×10cm.

so, 1 m³ = 10×10×10 = 1000 such cubes of 10cm side length = 1000 liters.

the pool is 5 m × 15 m × 1.5 m = 112.5 m³ = 112500 liters

we need 2 kg salt for every 10000 liters water, so we have how many units of 10000 liters in the pool ?

112500 / 10000 = 11.25

so, we need

11.25 × 2 = 22.5 kg salt

11.

12 seconds = 1/5 of a minute.

so, batman runs at 3 km / min (= 60×3 km/hour = 180 km/h - not possible in real life for any human being, but let's play ...) for 12 seconds = 1/5th of a minute, and so he runs 3km/5 = 600 meters in that time.

that means he has 2km - 600m = 1400m left to run in the 2 km race.

it takes him 1400/3000th of a minute (3000 m would take him the full minute)

1400 m × minute / 3000 m = 14/30 = 7/15 minutes

1/15th minute = 60 seconds / 15 = 4 seconds.

so, 7/15th of a minute = 7×4 seconds = 28 seconds.

the bionic woman runs the full 2000 m with 5 km / minute.

it takes her 2000/5000th of a minute

2000 m × minute / 5000 = 2/5th of a minute.

1/5th of a minute is 60 seconds / 5 = 12 seconds.

so, 2/5th of a minute is 12×2 = 24 seconds.

therefore, the bionic woman wins by 4 seconds (24 seconds vs. 28 seconds).

12.

there is enough food for 150 students for 5 days = 150×5 =750 "food units".

therefore, if there were only 100 students, the food would last 750/100 = 7.5 days.

and if the food runs out after 4 days it means there are

750/4 = 187.5 students (how much sense that makes to have half a student ...).

13.

x = the workload to be done

Michelle's work speed is x/6 days

Danielle's work speed is x/4 days

on each day working together they achieve

1× x/6 + 1× x/4 of the total work load.

that is

2x/12 + 3x/12 = 5x/12

so, they need 5x/12 × a days to finish the whole x.

5x/12 × a = x

5/12 × a = 1

5a = 12

a = 12/5 = 2.4 days to finish the whole work when working together.