Hi Guest!
Let the first term of the arithmetic progression be \(a_0\)
Let the common difference between two successive terms be \(d\)
Then, \(a_n=a_0+d(n-1)\)
The third term is when n=3:
\(a_3=a_0+2d\)
We are given that the third term is 94:
\(94=a_0+2d\) (Equation 1)
The 6th term is when n=6:
\(a_6=a_0+5d\)
Given that the 6th term is 85:
\(85=a_0+5d \) (Equation 2)
Subtract Equation 2 from Equation 1:
\(94-85=a_0+2d-a_0-5d \iff 9 = -3d \iff d=-3\)
Substituting in Equation 1:
\(94=a_0+2(-3) \iff a_0=100\)
The 15th term is when n=15:
\(a_{15}=a_0+14d=100+14(-3)=100-42=58\)
Hope this helped!