You can link to ZoneCalc or cite the website as a source using the below.
Link to ZoneCalc
Copy and paste:
<a href=”https://zonecalc.com”>ZoneCalc simple calculations</a>
Cite ZoneCalc
Copy and paste:
ZoneCalc.com: Find simple calculations such as multiplication, division and more. January 1, 2023.
Please note: you must use the date and year you read the source here. And, of course, make sure to use the correct link and title you are citing.