A/an measures engine speed by counting the number of ignition pulses.
a. timing light
b. odometer
c. tachometer
d. multimeter

The answer that fits the blank would be a TACHOMETER. The tachometer is an instrument which is utilized in the measurement of the speed of the engine in revolutions per minute or rpm. Typically, this is used in road vehicles. You can see the tachometer in the dashboard of your vehicle. Answer for this is C.

 these logs are all base 6
logx-2log2=4log2

logx-log2^2=log2^4

log-log4=log16
logx/4=log16
x/4=16 (multiply by 4 to both sides)
x=64