What triangle? Is there one on here?
It's dividing by 2.
Next 3 would be: 25, 25/2, 25/4 or converting those into decimals.
To find the output when you know the input, just plug the input into the function.
x+21=4+21=25
The output is 25.
Hope this helps!
Wait isn’t it 30 or am I reading it wrong?
