What is -10 (b-9) please​

Multiply -10 and b, and -10 and -9.

A negative and a positive equal a negative, but a negative and a negative equal a positive.

-10b+90

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hope it helps

-10(b - 9)        distribute by multiply -10 × b = -10b and -10 × -9 = 90

-10b + 90, final answer

I agree...C is the answer.  Anytime you put in a value for X, you get a different Y answer, so yes, there are many answers.  The other answer gives you two examples using x = 5 and x = 10.  You could also substitute any other number for x and get a different y answer; an infinite number of x's and y's actually.