$6 \int_0^{\pi/2} \sin t \cos t dt$

$4 \int_0^{\pi/2} \sqrt{9\cos^4 t \sin^2 t + 9\sin^4 t \cos^2 t} dt$

$12 \int_0^{\pi/2} \sin t \cos t dt$

$3 \int_0^{\pi/2} \sqrt{\cos^2 t + \sin^2 t} dt$