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The important thing here is not to panic at the sight of what looks like a complicated formula, but to use some common sense. The first formula you've quoted isThis formula is simply saying that however much oxygen the rat consumed in one minute, it will consume 60 times as much in an hour. That's pretty obvious, isn't it? This rat consumed 7.0 ml in 1 minute, so it will consume 7.0 x 60 = 420 ml in an hour.
The next bit is in two parts:which you can do by dividing the weight in grams by 1000, since there are 1000 g in 1 kg.... convert the weight data from g to kg
The first rat's weight was 249.3 g. So in kg, this is 249.3 1000 = 0.2493.
...and thenThis just says to divide the oxygen consumption per hour that we just worked out, by the rat's weight in kg. So that's 420 0.2493, which according to my calculator is 1684.7, to 1 d.p.use the formula
Metabolic rate = ml O2/hr
____________ = ml O2/kg/hr
That didn't hurt, did it?