Hey there!
Your expression is 8b. We know that when a number and a variable (or a variable and a variable) are together in one term, it means that they are multiplied. Usually, it is left in this form because we don’t know the value of the variable, but this time we do. It’s value is .5 as it says in the question. Therefore, we have:
b = .5
8b = 8*.5
8b=4
We can check our answer by dividing both sides by 8 which gives us b = 4/8 or 1/2 or .5
Your answer is 4.
Hope this helps!