Conditioning on length

1. Create a new version of your mass_from_length_theropoda() function from Part 1 of Exercise 1 called mass_from_length_max().
   • This function should only calculate a mass if the value of length passed to the function is less than 20.
   • If length is greater than 20, return NA instead.
2. Use sapply() and this new function to estimate the mass for the theropoda_lengths data from Exercise 1.