6. (15 points) Two identical resistors $R_{0}$ are connected in series and connected to a source of constant voltage. An ideal voltmeter is connected in parallel to one of the resistors. Its reading is $U=9 B$. If the voltmeter is replaced by an ideal ammeter, its reading will be $I=2$ A. Determine the value of $R_{0}$.
Answer: 90 m

Solution. The voltage supplied by the source is $U_{\text {total }}=2 U=18$ V. In the second case, the current flows only through one of the resistors. Therefore, $R_{0}=\frac{U_{\text {total }}}{I}=9 \Omega$.

## Qualifying Stage

## Variant 2

## Problems, answers, and evaluation criteria