First you must distribute the 4 to the numbers inside the parentheses, which would be 2 and 4b...
(4*2) + (4*4b) = 104
8 + 16b = 104
Now bring 8 to the right side by subtracting 8 to both sides (what you do on one side you must do to the other). Since 8 is being added on the left side, subtraction (the opposite of addition) will cancel it out (make it zero) from the left side and bring it over to the right side.
8 - 8 + 16b = 104 - 8
0 + 16b = 96
16b = 96
Next divide 16 to both sides to finish isolating b. Since 16 is being multiplied by b, division (the opposite of multiplication) will cancel 16 out (in this case it will make 16 one) from the left side and bring it over to the right side.
16b ÷ 16 = 96 ÷ 16
1b = 6
b = 6
Hope this helped!
~Just a girl in love with Shawn Mendes