Suppose you own 100 shares of CyberChase Corporation and 200 shares of NetSurfer Corporation. At the time of purchase, the stocks of CyberChase and NetSurfer were trading at $25 and $15 per share, respectively. What is the expected value of the portfolio if CyberChase has an expected return of 8 percent and NetSurfer has an expected return of 13 percent?

I know the answer is

Expected value of the portfolio =

$25*100*(1.08)+$15*200*(1.13)=$2,700+$3,390 = $6,090

I just don't understand why we used 1.08 instead of 0.08 and 1.13, instead of 0.13. What is the formula that says we have to add 1 to the expected return?