When you add a positive number and a negative number, how can you tell whether the sum will be positive or negative?

+ - = -

Step-by-step explanation:

+ (+) = +    

+ (-) = -

- (-) = -

- (+) = -

Two like signs become a positive sign

Two unlike signs become a negative sign

answer: 1.06 km per sec

step-by-step explanation:

39.6 m=63.72 km

60 min in an hour so 63.72/60=1.06