It’s 7 1/2 because 4x3 gives you the length of the bigger rectangle so, you multiply 2 1/2x3 and get 7 1/2 :)
This is how it is done. Let me know if you have questions...
<span>The doubling time is the period of time
required for a quantity to double in size or value. It is applied to
population growth, inflation, resource extraction, consumption of goods,
compound interest, the volume of malignant tumours, and many other
things that tend to grow over time.</span>
