I read this as 3x/8+1/3=7/12 in other words 3/8 of x plus a third equals seven twelfths.
One way to solve this is to multiply through by 24 (the LCD of 3, 8 and 12):
9x+8=14 because the denominators divide into 24 and the result is multiplied by the numerators. So 8 into 24 is 3 multiplied by 3x=9x; 3 into 24 is 8; and 12 into 24 is 2 multiplied by 7 is 14.
Subtract 8 from each side: 9x=6, x=6/9=2/3 or 0.667 to 3 decimal places.
Another way to solve it is to subtract 1/3 from each side: 3x/8=7/12-1/3=(7-4)/12=3/12=1/4. So 3x/8=1/4. Multiply both sides by 8: 3x=2 and divide both sides by 3: x=2/3.
Another way is, after getting 3x/8=1/4, write 1/4 as 2/8 then 3x=2, because we have eighths on both sides. So x=2/3.