While solving an equation for wavelength if you are given MHz as the frequency what do you multiply it by to transfer it to s^-1 or hz?

You need to multiply it by ##10^6##, or divide it by ##10^(-6)##.

You need to become familiar with metric prefixes, which are used to indicate either multiples of a basic unit, which in your case is Hertz, or **fractions of a basic unit.

You are given a frequency expressed in megahertz, or ##"MHz"##. As you can see in the above table, the mega- prefix is used to designate a multiple of the basic unit.

More specifically, mega- means one million times more than the basic unit. This means that if you take one hertz and multiply it by one million, or ##10^6##, you will get one megahertz.

Likewise, to go from megahertz back to hertz, you would have to reverse the process, i.e .divide by one million.

This means that if you divide one megahertz by ##10^6##, you get one hertz.

##"1 Hz" = "1 MHz"/10^6 = 10^(-6)"MHz"##

Therefore, to convert ##"99.5 MHz"## to ##"Hz"##, you would write

##99.5color(red)(cancel(color(black)("MHz"))) * "1 Hz"/(10^(-6)color(red)(cancel(color(black)("MHz")))) = 99.5 * 10^(6)"Hz" = 9.95 * 10^(7)"Hz"##

Alternatively, you can use the conversion factor

##"1 MHz" = 10^(6) * 1"Hz" = 10^(6)"Hz"##

to get the same result

##99.5color(red)(cancel(color(black)("MHz"))) * (10^6"Hz")/(1color(red)(cancel(color(black)("MHz")))) = 9.95 * 10^(7)"Hz"##