[tex]\\ \tt\hookrightarrow 2C_4H_10+13O_2\longrightarrow 8CO_2+10H_2O[/tex]
No of moles:-
[tex]\\ \tt\hookrightarrow \dfrac{Given\:mass}{Molar\:mass}[/tex]
[tex]\\ \tt\hookrightarrow \dfrac{400}{58}[/tex]
[tex]\\ \tt\hookrightarrow 6.89mol[/tex]
Now
Moles of O_2
[tex]\\ \tt\hookrightarrow 7.5(6.89)=51.6mol[/tex]
Mass of O_2
[tex]\\ \tt\hookrightarrow 51.6(32)=1651.2g[/tex]