Minority interest of acquired company

At 45% ownership it will almost certainly be reported using the equity method of accounting, which means Company A will not report any minority interest. Company A will report a single line item called "Equity Method Investments" or something similar as an asset on its balance sheet. This will be recorded at cost and will increase with Company A's share of Company B's net income, and will decrease with dividends paid from Company B to Company A.

What happens Company B's balance sheet depends on how the deal is structured. If Company A gets its 45% ownership from newly issued shares, than it's just like any normal secondary offering of equity: cash will go up by the amount invested and capital will go up by the same amount. If Company A purchased its stake on the open market (i.e., not via a new issue of shares, but just by buying 45% of the outstanding shares) then nothing happens to Company B's balance sheet. They just have new owners for 45% of their stock.