Please answer either or all of them and please show me how you solve it

Step-by-step explanation:

using pythagoras theorem

a^2 + b^2 = c^2

4^2 + y^2 = 21^2

16 + y^2 = 441

y^2 = 441 - 16

y^2 = 425

y = 13.2

a^2 + b^2 = c^2

4^2 + x^2 = 7^2

16 + x^2 = 49

x^2 = 40 - 16

x^2 = 33

x =

x = 5.7 m

answer: -8.2562234e+13

54 kilometers per hour

step-by-step explanation:

according to rules:

1 km = 1000 meter

which means that 1 meter = 1/1000 km

1 hour = 3600 second [ as 1 hour = 60 min = 60 *60 seconds ]

which means that 1 second = 1/3600 hour

therefore, 1 kilometer/hour =

thus to convert 15 meter per second to kilometer per hour, we multiply 15 to 3.6 kilometer/hour.

15 meter/second=   which is the required answer.