I think it would be -12, use the infinite geometric series equation :
For this equation, it would be: x / ( 1 - 0.5x^2)
set this equation to equal -12, you will get 2 different x answers x = -4/3 and x = 3/2, however, one is eliminated
x = - 1 (1/3 )
Credit : Melody
Link : https://web2.0calc.com/questions/kevin-kangaroo-begins-hopping-on-a-number-line-at