Time

Time uses a chain of units.
$60$ seconds $= 1$ minute, $60$ minutes $= 1$ hour, and $24$ hours $= 1$ day.
Because the steps are fixed, you can convert between them by multiplying or dividing.

To change a larger unit into a smaller one, multiply.
For example, $2$ hours $= 2 \times 60 = 120$ minutes.
To go the other way, divide: $150$ minutes $= 150 \div 60 = 2$ hours $30$ minutes.

To find elapsed time, count from the start time to the end time in steps.
From $9:50$ to $1:20$, first go to $10:00$ (that is $10$ minutes), then to $1:00$ (that is $3$ hours), then to $1:20$ (that is $20$ minutes).
Altogether that is $3$ hours $30$ minutes.

Time also appears in rate problems, where $\text{distance} = \text{speed} \times \text{time}$.
Rearranged, $\text{time} = \frac{\text{distance}}{\text{speed}}$.
So a trip of $150$ miles at $50$ miles per hour takes $\frac{150}{50} = 3$ hours.

How many minutes are in $2$ hours $45$ minutes?
Convert the hours to minutes: $2 \times 60 = 120$ minutes.
Add the extra $45$ minutes: $120 + 45 = 165$ minutes.

A movie starts at $7:40$ PM and ends at $9:25$ PM. How long is it?
From $7:40$ to $9:40$ is $2$ hours.
But it actually ends at $9:25$, which is $15$ minutes before $9:40$.
So the movie runs $1$ hour $45$ minutes.

A cyclist rides $36$ miles at a steady speed of $12$ miles per hour. How long does the ride take?
Time is distance divided by speed.
So it takes $\frac{36}{12} = 3$ hours.