What would be the percentage is the non-singing trait in female birds in generations, four and five if this pattern continues

Generation 4: 74%
Generation 5: 82%
The percentages of the first three generations:
G1: 50%
G2: 58%
G3: 66%
The percentages go up by 8% with each generation (G). Therefore to find the next generation add 8 to the previous generation.
66 + 8 = 74
G4 = 74%
74 + 8 = 82%
G5 = 82%