The rule for the number of fish in a home aquarium is 1 gallon of water for each 1 inch of fish length. marta's aquarium 13 gallons and hanks aquarium holds 17 gallons. based on the number of fish they bought in exercise 10 ( marta got 3 guppies & 2 planties; hank got 3 guppies & 4 planties) how long is a guppy and how long is a planty?

Ok so 1gallon=1

guppylegnth=g
plantielegnth=p

martha has 13 inches of fish
hank has 17 inchs of fish

the amount of fish is calculated by
amount of each fish times legnth of fish

martha:
13=3g+2p

hank:
17=3g+4p

compare, asssuming that all planties are same legnth and all guppies are same legnth

13=3g+2p
17=3g+4p
looks like we just added 2p to first euation to get secon equation

minus them
-13=-3g-2p
17=3g+4p +
4=0g+2p

4=2p
divide 2
2=p

sub back

13=3g+2p
13=3g+2(2)
13=3g+4
minus 4
9=3g
divide 3
3=g

guppies are 3 inches
planties are 2 inches
9