twelve less then -9 times a number is equal to 8 minus 4 times the number

If you let 'n' to represent a number then '-9 times a number' can be written as -9n

'less then' means subtraction:  12 less then -9 times a number  becomes -9n - 12 (the subtraction in the equation is written in the opposite way as written in words)

'8 minus 4 times the number ' becomes 8 - 4n

So, the equation is:  -9n - 12  =  8 - 4n

Get all the variables to one side. If you add  9n  to both sides:

    -9n + 9n - 12  =  8 - 4n + 9n

    -12  =  8 + 5n

Subtract 8 from both sides:

    -12 - 8  =  8 - 8 + 5n

    -20  =  5n

Divide both sides by 5:

    -20 ÷ 5  =  5n ÷ 5

    -4  =  n

Now, check the answer:   -9n - 12  =  8 - 4n

               -9(-4) - 12  =  36 - 12  = 24                 8 - 4(-4)  =  8 + 16  = 24        They check!