Given:
production of electricity in Minnesota in 10^9 kWh
in 2009 = 12 (renewable) = 15% of total production (P)
in 2015 = 25% (renewable) of total production (P)
Total production of the two years are the same.
Solution:
First find P
we know that 12 * 10^9 kWh is 15% of P, or
0.15P=12*10^9
=> P=12*10^9/0.15 = 80*10^9 kWh
For 2015,
25% of P is renewable, therefore
x=0.25P=0.25*80*10^9 kWh = 20 * 10^9 kWh
Hence answer is 20, in units of 10^9 kWh.