數學(一元一次方程式)

20000*(1+R%/4)^2=1218

(1+R%/4)^2 = 1218 / 20000
(1+R%/4) = (1218 / 20000^1/2
= 0.2468
R%/4 = -0.7532

R should not be negative as I think it represents interest rate.
Furthermore, I think the number on left hand side of the question should be 20000+1218 i.e. 21218 after including the original deposit instead of 1218:

20000*(1+R%/4)^2=21218

(1+R%/4)^2 = 21218 / 20000
(1+R%/4) = (21218 / 20000^1/2
= 1.03
R%/4 = 0.03
R% =0.12

Therefore, R=12

12 !!!!!!!1