Answer:
36.73%
Explanation:
Let x = 100
13% increase = 100(1 + 0.13) = 100 + 13 = 113
21% increase = 113(1 + 0.21) = 113 + 23.73 = 136.73
Hence, a single percentage to arrive at 136.73 will be :
x
100(1 + x) = 136.73
100 + 100x = 136.73
100x = 136.73 - 100
100x = 36.73
x = 36.73 / 100
x = 0.3673
0.3673 * 100% = 36.73%