To find out how many years it will take for the plates to collide, we can use the formula:
\[ \text{Time} = \frac{\text{Distance}}{\text{Rate}} \]
Here, the distance between the two plates is given as 1,500 km, which we need to convert into centimeters because the rate of movement is in cm/year.
1 kilometer is equal to 100,000 centimeters, so:
\[ 1,500 \text{ km} = 1,500 \times 100,000 \text{ cm} = 150,000,000 \text{ cm} \]
Now, we can calculate the time it takes for collision using the rate of 3 cm/year:
\[ \text{Time} = \frac{150,000,000 \text{ cm}}{3 \text{ cm/year}} = 50,000,000 \text{ years} \]
Therefore, the plates will collide in 50,000,000 years.