Note that 4a6 is a mixed fraction.
4a6= (6×4) +a6= 24 +a6
Given, (24+a)6 = 276
Comparing the numerators on both sides, we get 24+a=27
Therefore, a=(27−24)=3
If 15sin4a+10cos4a=6, find the value of 8cosec6a−27sec6a.