Let the CP of the article be Rs.x
(SP-CP)*100/CP = -29, or
-29CP = 100SP - 100CP, or
100 SP = 71 CP = 71x or
SP = 0.71x.
If the SP was Rs.84 more than the profit would be 11%..
Revised SP is 0.71x + 84
Revised profit = 11% or (0.71x+84-x)*100/x = 11, or
11x = 71x+8400–100x, or
100x+11x-71x = 40x = 8400, or
x = 8400/40 = 210.
The Cost Price was Rs.210.