I love 'think of a number' activities as they give your brain a really good work-out.

To tackle them you need to work backwards and use the inverse.  Remember that division and multiplication are friends and, so too are  addition and subtraction.  When you know this then you know, for example,  that 7 multiplied by 8 is 56 (7 8s are 56! 5! 6! 7! 8!) and 56 divided by 8 is 7

William says:
'I am thinking of my favourite number. If I add 6 to my number then divide the result by 2, the answer is 21'
What number was William first thinking of?

 Jane says:
'If I multiply my number by 3 then add 6 then add 3 then add 4 the answer is 76'
What number was Jane first thinking of?

Christopher says:
'If I divide my number by 5 and add 6 the answer is 16'
What number was Christopher first thinking of?

Daniel says:
'Can you guess what number I am thinking of if when I multiply it by 5 and add 6 the answer is 106?'
What number was Daniel first thinking of?

Sophie says:
'I think of a number. I multiply my number by 3 and add 4 the answer is 37'
What number was Sophie first thinking of?

Ethan says:
'I am also thinking of a number. If I multiply my number by 2 and add 3 the answer is 23'
What number was Ethan first thinking of?

Have a go and let me know how you get on. If you struggled - don't worry. The comments feature is completely private until I publish them.  This means that if you do find it tough then only you, your grown-ups and I only need to know.