correct answer is: d) ₹1054

Here,
Principal =₹ 640
Amounts =₹ 768
Time = 2 years 6 months or \left(2+\frac{6}{12}\right) or \frac{5}{2} years
\therefore S.I. =\left(amounts\ -\ principle\right)
\rightarrow S.I. =₹\left(768\;-\;640\right)
\rightarrow S.I. =₹ 128
We know, Rate =\frac{100\times S I}{P\times T}
\rightarrow R =\frac{100\times128\times2}{640\times5}
\rightarrow R = 8 %
According to the question,
New Principal =₹ 850
New Time = 3 years
So that,
The S.I. of ₹ 850 in 3 years is =\left(\frac{p\times r\times t}{100}\right)
\rightarrow New S.I. =\left(\frac{850\times8\times3}{100}\right)
\rightarrow ₹ 204
\therefore New amount in 3 years will be \left(principle+S.I\right)
\rightarrow₹\left(850+204\right)
\rightarrow₹ 1054
Ans: In 3 years at the same rate percent per annum the amount will be ₹ 1054.