The given function is:
f(x) = 1.5x + 7
Then, since x represents the age of the baby, in months, in order to find its weight with 5 months, that is, f(5), we need to replace x by 5 in the above equation:
f(5) = 1.5 * 5 + 7 = 7.5 + 7 = 14.5
Therefore, the last option is correct.