Answer
Please see the work below.
Work Step by Step
We know that the frictional force is given as:
$f=\mu N$
$\implies f=\mu (0.7M)g$
To find out the maximum acceleration, we equate this to $Ma$
$\implies \mu(0.7M)g=Ma$
This simplifies to:
$a=\mu(0.7)g$
We plug in the known values to obtain:
$a=(0.61)(0.7)(9.8)$
$a=4.2\frac{m}{s^2}$
