Permabanned
Without any info about the depth of the indent, I can’t see anyway to solve this.
You have the size of the indent. It's 20 minus the 4 and 5, leaving the "gap" number, 11.
I guess you have to, since it's year 7 maths and not a technical drawing
You can't make that assumption though
Assuming didn't land us on the moon though did it.
This.Return to the teacher with a note "My dad said this is impossible to work out unless we assume the indent is square, but assumption didn't get us to the moon"