Hi Kundan!
The outputs for DSC11 & DSC12 are strings, not integers. So if you wanted to extract a number from those fields, are you just wanting to capture the first number in the selection? So if someone selects "5 - For value more than...", you'd want the sum to capture the value "5" and then add that to the rest of the formula, correct?
If that's the case, I'd recommend seeing if the following would return a value:
SUM(DSC1,DSC2,DSC3,DSC4,DSC5,DSC6,DSC7,DSC8,DSC9,DSC10,IF(ISBLANK(DSC11)&&ISBLANK(DSC12),0,IF(ISBLANK(DSC11),NUMBER(LEFT(DSC12,1)),NUMBER(LEFT(DSC11,1)))))
The "IF" statements first checks to make sure that there's a value in one of the fields - if no value is found, it returns "0". From there, it tries to configure a value for the option selected, by grabbing the first LEFT character of the selection, then forcing it into a NUMBER.
I tried to test the formula in our own environment but we don't have any fields where the selections begin with a value, so I figured it might be easier to just have you test it and we can troubleshoot from there.