Final answer:
To evaluate x * y when x = 3.9 and y = 0.42, the expression simplifies to 1.638.
Step-by-step explanation:
To evaluate the expression x * y when x = 3.9 and y = 0.42, we simply substitute these values into the expression.
So, x * y = 3.9 * 0.42 = 1.638.