b(x) = |3-x|+1
b(10) means that we need to replace x by 10:
b(10) = |3-10|+1
As you can notice, 3-10 is between the lines of the absolute power. So if the answer is positive, you keep positive. If the answer is negative, you transform it to positive. |a| = a and |-a| = a. So |a|=|-a|.
So |3-10| = |-7| = |7| = 7.
b(10) = |3-10|+1 = 7 + 1 = 8.
So the value of b(10) when b(x)=|3-x|+1 is 8.
Hope this Helps! :)