Return on asset is 18.46 percent
Explanation:
Given information's are
Return on equity of Google inc., = 12.00% ( google inc does not change it's capital structure so return remains at  12%)
debt-to-equity ratio =  30.00 percent
 Percentage return on assets of Google, Inc
Return on asset = Net income ÷ average total assets     
debt-to-equity ratio = Total liabilities ÷ stake holder's equity
here no amount is given for any account let us make an assumption as follows.,debt-to-equity ratio =  30.00 percent
The stack holder's equity  is $100 ( 30 ÷ 100 = 0.30 or 30 percent)

 Total Assets considers both Equity and Debt       
so the Average assets = (debt + equity)÷ 2  
Average assets = ($30 + $100 ) ÷ 2 = $65

Net income is the return attributed to the equity holders here., 
$100 be the share holders equity get from debt-equity ratio
Return on equity = 0.12 = Net income ÷ share holders fund
Net income = 12 percent = $100 × 12÷100 = $12 

Return on asset = Net income ÷ average total assets 
Return on asset  = 12÷ 65 = 0.1846 or 18.46 percent
