To find how many movies streamed would result in both streaming plans costing the same amount, let's set up equations based on the given costs of each plan.
Let \( x \) be the number of movies streamed in a month.
Cost for Plan A: \[ \text{Cost of Plan A} = 15 + 4x \]
Cost for Plan B: \[ \text{Cost of Plan B} = 9 + 6x \]
Now, we want to find the value of \( x \) that makes the two costs equal:
\[ 15 + 4x = 9 + 6x \]
To solve for \( x \), first, subtract \( 4x \) from both sides:
\[ 15 = 9 + 2x \]
Next, subtract 9 from both sides:
\[ 6 = 2x \]
Now, divide both sides by 2:
\[ x = 3 \]
Thus, both plans would cost the same amount when 3 movies are streamed.
Answer: 3 movies