[R] transform

[Val]

Hi all,
I want to standardize  a variable based on certain condition
Here is my sample of data

obs, Year, bb, kk,  y
1,  2001, 25 ,100, 12.6
2,  2001,  15 ,111, 24.7
3,  2001,  53, 110, 13.8
4,  2001,  50, 75,  9.6
5, 2001,  125, 101, 31.5
6,  2001,  205, 407, 65.7
7,  2001,  250, 75, 69.1

If the value of "bb" is  greater than 75 and the value of "kk" is
greater than 100 then I want get  the mean and STD values of "y".  In
this example obs 5 and 6 satisfy the condition.  The mean is 48.6 and
STDEV is 24.18
Then I want to transform the "y" values  with  mean = 10 and SDTEV of 3.
 w= ((y- 48.6)/24.183)*3 +10

My question, how can i pas those mean  and STDEV values  to create the
new variable (w)?

The result looks as follows

obs, Year, bb, kk,  y,     w
1, 2001, 25 ,100 , 12.6,  5.534062435
2, 2001, 15, 111,  24.7,   7.035113672
3, 2001, 53, 110, 13.8,   5.68292702
4, 2001, 50, 75,   9.6,    7.642977396
5, 2001, 125, 101, 31.5,   7.878679656
6, 2001, 205, 407, 65.7,  12.12132034
7, 2001, 250, 75 , 69.1, 12.54310334

Thank you in advance