Answer:
The area can be found by multiplying the two terms, and the perimeter by doubling and adding them.
Using this, we find that the area of the rectangle is 60x³, and the perimeter is 10x² + 24x.
Step-by-step explanation:
First let's find the area:
5x² × 12x
= 60x³
Now the perimeter:
2(5x² + 12x)
= 10x² + 24x
In the old aquarium, 3 tablespoons of salt were used for 20 gallons. That's a conversion ratio of

That is, for every gallon of water in the aquarium, there was 0.15 tbsp of salt. So a 50 gallon aquarium, Ill should add

to maintain the salinity.