# A voltage of 180 V is placed across a substance. The current begins higher, but as the substance's temperature changes it falls to 6 A. What is the resistance of the substance at this point?

The resistance is $30$ $\Omega$ when the current has decreased to $6$ $A$.
There is a law for the relationship between current and resistance, called Ohm's Law, $V = I R$. First find the applied voltage: $V = I R = 10 \times 18 = 180$ $V$. Then $R = \frac{V}{I} = \frac{180}{6} = 30$ $\Omega$.