How to subtract a number(174)to a percentage(30%)

I'm not entirely sure what your exact question is, so I will answer multiple questions, hopefully one of them is yours.  

If you want to calculate a number that is 30% less than 174, you multiply 174 by (100-30)%.  So, 174 x 70% or 174 x 0.7 = 121.8

If you want to calculate a number that is 30% of the value of 174, you multiply 174 by 30%, or 174 x 0.3 = 52.2

If you want to know what number has 30% of its total equal to 174, you divide 174 by 30%, or 174/0.3 = 580.  Therefore, the number 174 is equal to 30% of the number 580.  

I hope one of those helped

You change 30% into a decimal number which is .30 or .3 then you subtract it from 174 which is 173.7