mean difference test with 3 groups for 2 periods separately

[Yapa Bandara]

Hello,
this is an abstract of my data set. I need to do a ttest for means of investment between high and low income groups, and need to do this separately for pre and post policy periods. Can you please help me with this? Many thanks in advance

Investment	Income	post/pre policy (post =1, pre =0)
20000	High	1
480000	High	0
15000	Mid	0
3000	Low	0
9000	Low	1
6000	Low	0
12000	Mid	1
24000	Mid	1
80000	High	1

[George Ford]

ttest investment, by(income)
ttest investment, by(policy)

there are several options (equal variance, etc).

or could use regression so you can use robust or other methods.

reg investment i.income
reg investment policy