First distribute -6 to 3b and -1.
-6(3b - 1) = -18b+6
So now you have 55 -18b + 6 = -11. Now you want to start isolating to solve for b. Subtract 6 from both sides.
55 -18b + 6 = -11
-6 -6
Now you have 55 -18b = -17. Then subtract 55 from both sides.
55-18b = -17
-55 -55
That leaves you with -18b = -72. Now divide both sides by -18 to solve for b. Remember that a negative divided by a negative gives you a positive.
-18b ÷-18 = -72 ÷ -18
Leaves you with b = 4. Now plug 4 back into the equation for b to see if it's true. 55 - 6(3(4)-1) = -11. It works, so it's true.
