4⁻⁴＋4⁻⁴ = 4ˣ

2⁻⁸＋2⁻⁸ = 2²ˣ

2⁻⁸⁺¹ = 2²ˣ

x = －3.5

12.25 = y／2

y = 24.5

24.5－3.5 = 21