let

h = the number of hippos

b = the number of birds

you see a total of 42 animals

h + b = 42

since every hippo has 4 legs and each bird has 2 legs and the total of legs is 114 we have

4h + 2b = 114 divide both sides by 2

2h + b = 57

by solving the system of equations

h + b = 42

2h + b = 57

we find

h = 15 hippos

b = 27 birds

click here to see the step by step solution of the system of equations

Click to see all the steps

there were 15 hippos.