simply replace the unit of measurement you don't want, with it's conversion in the measurement you do want and simplify
example. say we want to convert 32 feet to inches.
we know that 1 ft = 12 inches. that is, wherever i see the unit "ft" i can replace it with "12 in"
so, 30 ft = 30 (12 in) = 30*12 in = 360 in
we relate the conversion factors in terms of ratios, in such a way that the units we don't want cancel out, and the units we do want stay.
lets do the previous example using this method.
we know 1 ft = 12 in. to put this in a ratio, we can write it as either or , depending on what we want to convert from.
lets say we want to, again, convert 30 ft to inches, so we write down 30 ft
now we want to multiply this by one of the ratios above to get it in inches. since we want the ft units to cancel out and the inches unit to stay, i want the ft unit in the denominator to cancel the ft from the 30 ft, and leave the in unit in the numerator. that is, we write
now the ft unit cancels, and we are left with
and that's it. now try to do the problems yourself and post your answers. note that if you are adding quantities, you need them to be in the same units. so if you want to sum 35.0 ft, 1.35 ft, 72 in., and 48.69 ft, you must first convert that 72 in to ft. then add them. then you can convert the answer to meters for part (b)