The number of terms in the binomial expansion of an expression of the form (a + b)n is given by the formula n + 1, where n is the exponent.
In this case, we have the expression (3x + b)59. Here, n is equal to 59. Thus, to find the number of terms in the binomial expansion, we plug n into the formula:
59 + 1 = 60
Therefore, there are 60 terms in the binomial expansion of 3x59.