Certain rides at the fair exhibit periodic motion such as the Ferris wheel. List some other machines that you have observed that show repetitive motion

Some examples are:

BlendersWatchesHydrulic hammersBall millsElectric saws

Explanation:

Many devices and tools that you see or use daily are examples of repetivie motion:

Blenders:

the rotary movement of the blades of a blender is repetitive because it makes the same journey continuously.

Watches:

the clock hands repeat their movement throughout the day: the second hand every 60 seconds, the minute hand every 60 minutes, and the hour hand every 12 hours.

Hydrulic hammers

this tool drills holes or breaks rocks by knocking incessantly at an impressive rate: the tip goes down and goes up a large number of times per second.

Ball mills

ball mills grind by rolling the internal spheres over the materials that want to be crushed by continuously rotating the mill.

Electric saws

the sharp saw makes a continuos circular motion at high speed to cut the materials.

A) Action: multiply both sides by 4. 

Have a look: 

(x/4)x4=16x4 
x=64 

As you can see, the value of x can be found by multiplying 4 on both sides.

Hope I helped :)