I dont understand how to use the table to answer ..the quistion

(a) Express a period of 100 ms in microseconds.?

I need more explanation how the answer comes by this way ??

Also the second question (b)

Unit Equivalent Unit Equivalent seconds (s) 1 s hertz (Hz) 1 10-3 s kilohertz (KHz) milliseconds (ms) 103 Hz 106 Hz microseconds (us) 10-6 s megahertz (MHz) nanoseconds (ns) 10-9 s gigahertz (GHz) 109 Hz 10-12 s terahertz (TH 1012 Hz picoseconds (ps) units of period and respective frequency (a) Express a period of 100 ms in microseconds. 100 ms 100 x 103 s 100 x 10-3 x 106 us 105 us (b) Express the corresponding frequency in kilohertz. 100 ms 100 x 10-3 s 10-1 s f 1/10-1 Hz 10 x 10-3 KHz 10-2 KHz