Answer
$-\frac{320}{13}$ degrees Celsius or $-\frac{160}{13}$ Fahrenheit.
Work Step by Step
Setting $1.8C+32 = 0.5C$, we get $1.3C = 32, C = -\frac{320}{13}$, so the temperature is $-\frac{320}{13}$ degrees Celsius or $-\frac{160}{13}$ Fahrenheit.