To find the average speed, you can use the formula:
\[ \text{Average Speed} = \frac{\text{Distance}}{\text{Time}} \]
Monica rode her bike 35 kilometers in 2.5 hours. Plugging in the values:
\[ \text{Average Speed} = \frac{35 \text{ km}}{2.5 \text{ hours}} = 14 \text{ km/h} \]
So, Monica's average speed was 14 kilometers per hour.