To find out how many levels Britney should beat today, we first need to determine her rate of beating levels per minute.
Yesterday, she played for 27 minutes and beat 3 levels. We can calculate her rate as follows:
\[ \text{Rate} = \frac{\text{Number of levels}}{\text{Time in minutes}} = \frac{3 \text{ levels}}{27 \text{ minutes}} = \frac{1}{9} \text{ levels per minute} \]
Now, if Britney plays for 45 minutes today at the same rate, we can calculate how many levels she should beat:
\[ \text{Levels beaten today} = \text{Rate} \times \text{Time in minutes} = \frac{1}{9} \text{ levels per minute} \times 45 \text{ minutes} \]
Calculating this gives:
\[ \text{Levels beaten today} = \frac{45}{9} = 5 \text{ levels} \]
Therefore, Britney should beat 5 levels today.