Answer: a - (9xb)
Step-by-step explanation:
"A number diminished"
Diminished means made smaller or less.
So a variable minus.....
"By 9 times a number"
"By" with (including the variable multipled with 9)
"9 times a number" 9 multipled by a variable in parenthesis.
So 9 times a variable.
I hope you got it right :)
