Calculating Circuit Delay
The answer to the first question is that if you take max(max(t,mt)+t,mt)+t, you can bring the t in the inner brackets, obtaining max(t+t, mt+t): since the latter is always bigger than mt (unless you have a negative t) you can simplify with max(t+t, mt+t)+t and then take out again the +t and obtain the value shown.

For the second part, m is again the coefficient that multiplies t: let's take your case.

m=7, so max(t, 7t)+2t=9t as shown.

It's easy!