Angelina's italian restaurant has collected data about customer sauce orders. it calculated that p(pesto) = 0.42, p(alfredo) = 0.86, and p(pesto or alfredo) = 0.93. determine the p(pesto and alfredo).

Here's what we know:

There's a 0.42 chance someone will order pesto.
There's a 0.86 chance someone will order alfredo.
There's a 0.93 chance someone will order pesto or alfredo.

So what's the chance that someone ordered both?
Well, subtract 0.86 from 0.93 and you'd get 0.07.
That's the chance someone will order only pesto.
The rest of the 0.42 must have been from those who had both.
0.42 minus 0.07 is 0.35.