Tolong bantu ya, soal di gambar, pakai caranya

r/t=3/4
t=4r/3
s=akar dr r^2 + t^2
=akar dr r^2 + (4r/3)^2
=akar dr r^2 + 16r^2/9
=akar dr 25r^2/9
=5r/3
Lselimut=phi x r x s
423,9=3,14 x r x 5r/3
423,9=15,7r^2/3
r^2=423,9x3/15,7
=81
r=akar dr 81=9