Our company is kept going by the investments of our country and our firm.
It's the investments of our country and our firm that make the company viable.
「成り立つ」は「to consist of, to be made up of」という意味もありますが、この場合では「to keep going, to be viable」という意味になるでしょう。
受動態でも受動態でも使えます。
例文１は受動態です。ほかの例文は
Our company is made viable by the investments of our country and our company.
能動態は例文２とこれです：
The investments of our country and our company keep the company going.
「keep it afloat」も言えます。会社が船になった隠喩です。
The company is kept afloat by investments.
アメリカ合衆国 
