Which of the following is a complex number?

You'll be disappointed to find out these are *all* complex numbers, because the set of real numbers is a subset of the complexes.

Probably the question means to ask, "which of these numbers is strictly non-real?" in which case D would be the answer because it contains the square root of a negative number that introduces the imaginary unit i. All the other options are strictly real numbers.

for b its (t) and c its (d)

step-by-step explanation:

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.