let us convert each of the numbers in base b,(b-2),8 into decimal numbers.
$142_b+112_{b-2}=75_8$
$2+4*b+b^2+2+b-2+(b-2)^2=5+8*7$
$2+4b+b^2+b+b^2+4-4*b=61$
$2b^2+b-55$
From the given options, only b=5 satisfies the above equation.
So it is the answer.