Condition of SHM is stated below,
Acceleration is directly proportional to negative of displacement of particle.
If ‘ $\mathrm{a}$ ‘ is the acceleration,
$\mathrm{x}$ is the displacement
Then, for Simple Harmonic Motion,
$\mathrm{a}=-\mathrm{kx}$ where $\mathrm{k}$ is constant
(a) $a=0.7 x$
This is not in the form of $a=-k x$
So, it is not SHM
(b) $a=-200 x^{2}$
Clearly we can see, it is not SHM