-2
20 greater than 8x +5 is ...
... 8x +5 +20 = 8x +25
We want this value to be -3(2x +1), so we want to solve the equation ...
... 8x +25 = -3(2x +1)
... 8x +25 = -6x -3 . . . . . . eliminate parentheses
... 14x = -28 . . . . . . . . . . . add 6x-25
... x = -2 . . . . . . . . . . . . . . divide by the coefficient of x
The desired value of the variable is -2.
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Check
-3(2x+1) = -3(2(-2)+1) = -3(-3) = 9
8x+5 = 8(-2) +5 = -11
9 is 20 greater than -11, so the answer checks OK.