How do i add a few numbers from dynamic text boxes?

ok so i searched the forum an i cant really figure it out

i have some numbers load from an external text file into a few dynamic text boxes, ok so lets call them scoreA, scoreB, an scoreC. An say i want those numbers to all add up into a dynamic text box named SCORE.

now ive seen something about Number(string); to make the numbers in the boxes real numbers because they only add like 3+4= 34 instead of 3+4 =7. But for one where does that Number(string); go or how does it work?? an then once that is complete what should the script look like to add all 3 to equal in another dynamic text box. thank your very much if can help me