Question

So can someone walk me slowly through this "solution" to fill in the blanks please.

Answer 1

The file attached shows the so called workings - but again the nuisance is most of the hidden steps.

Answer 2

I can see the point of the second line as it attempts to get the second integral expression back to the form that allows substitution by the \[\exp^\left( - \lambda t\right)/-\lambda\] above.

Answer 3

What I don't get is the rule that brings 1/lambda out and move t to the other factor