Thus, each volcano independently chooses one of 3 levels, so total distinct ordered assignments: $3^4 = 81$. But if profiles are considered unordered across volcanoes (e.g., just the count distribution), then we must count the number of integer solutions to $x_L + x_M + x_H = 4$, $x_i \geq 0$, which is $\binom4 + 3 - 13 - 1 = \binom62 = 15$. - Nelissen Grade advocaten