Step 1: Recall the relation between power, work, and time.
Power is defined as work done per unit time:
\[
P = \frac{W}{t}
\]
or, rearranging,
\[
W = P \times t
\]
Step 2: Represent in given symbols.
If the units of power, work, and time are \( x_1, x_2, x_3 \) respectively, then:
\[
x_2 = x_1 \times x_3
\]
Step 3: Conclusion.
Hence, the correct relation is \( x_1 \times x_3 = x_2 \).