The answer is **C: 13.5%**.
To calculate the percentage of Rhesus monkeys that weigh less than 7200 grams, we can use the standard normal distribution. The standard normal distribution is a bell-shaped curve with a mean of 0 and a standard deviation of 1. We can use a z-table to find the probability that a standard normal variable is less than a certain value.
To calculate the z-score of a Rhesus monkey's weight, we can use the following formula:
```
z = (x - μ) / σ
```
where:
* x is the Rhesus monkey's weight
* μ is the mean weight of the Rhesus monkeys (7700 grams)
* σ is the standard deviation of the Rhesus monkeys' weights (250 grams)
For a Rhesus monkey that weighs 7200 grams, the z-score would be:
```
z = (7200 - 7700) / 250 = -2
```
We can then use a z-table to find the probability that a standard normal variable is less than -2. This probability is approximately 0.135.
Therefore, the percentage of Rhesus monkeys that weigh less than 7200 grams is approximately 13.5%
```
13.5
```