help with this

Eric is studying the growth of a particular type of plant. He is testing the effects of four growth factors; lighting, age, temperature, and humidity. Here are the levels he's testing for each. Growth factor Levels Lighting None, Low, Medium, High Age 1 month, 2 months, 3 months, 4 months Temperature 20 .C, 22 .C, 24 .C Humidity Low, Medium, High He wants to find the number of ways of combining one level from each of the growth factors, How many ways are there