A1 gram spiders sits on a platform rotating at 78 rpm. the spider is 15 cm from the centre disk. find the speed of the spider

The spider is traveling in a circle with radius = 15cm

The circumference of any circle = 2 pi (radius)
The circumference of the spider's path = 2 pi (15 cm) = 30 pi cm

The spider completes a trip around this path 78 times per minute.
Its speed, relative to you, is   

                               (78) x (30 pi) cm/min =

                                       2,340 pi cm/min =  7,351.33 cm/min =

                                       73.5133 meter/min =

                                       4.411 km/hr =

                                         2.74  miles/hour

(After the last appearance of pi,
all numbers are rounded.)