Soulver can use your Macs default voice to speak out your current expression and answer.
Highlight one or more lines and choose Edit > Speech > Speak Selected Lines.
Soulver will read out your expression and answer together in the form of "One plus one is two".
Tips
Soulver can read out an entire times tables really easily. Type "1 × 7" and Soulver will read "One times seven is seven.