Answer
$6.5$
Work Step by Step
To solve the given equation for $a$, we move out the term $v_i$ and then divide both sides by $t$ as follows
$$
v_f=v_i+at\Longrightarrow v_f-v_i=at \Longrightarrow a=\frac{v_f-v_i}{t}
.$$
Now, by substitution, we have
$$
a=\frac{v_f-v_i}{t}=\frac{88-10.0}{12}=6.5
.$$
