Note the equal sign. What you do to one side, you do to the other.
Do the opposite of PEMDAS.
First, subtract 4.6 from both sides
3.1x + 4.6 (-4.6) = 10.8 (-4.6)
3.1x = 10.8 - 4.6
3.1x = 6.2
Isolate the x. Divide 3.1 from both sides
3.1x/3.1 = 6.2/3.1
x = 6.2/3.1
x = 2
C) 2 is your answer
hope this helps