Hi! I'm happy to help!
First of all, we need to substitute b into the expression.
6(2b-4)
6((2×5)-4)
Now we use the order of operations, or PEMDAS (Parenthesis, Exponents, Multiplication or Division, and Addition or Subtraction) to finish simplifying.
We see that 2×5 is inside two sets of parenthesis, so we solve that first
6((2×5)-4)
6((10)-4)
We cam remove the extra set of parenthesis because there isn't an expression inside of it any more.
6(10-4)
Now, we look inside of the parenthesis again and we see 10-4
6(10-4)
6(6)
The six next to the parenthesis has no sign next to it, which means to multiply.
6×(6)
Now we can remove the parenthesis.
6×6
Now, we just simply multiply.
6×6
36
To sum it up: The value of 6 (2b-4) When b=5 is 36
I hope this was helpful, keep learning! :D