we have
[tex]5,15 \\6, 18 \\7,21 \\8,?[/tex]
Let
[tex]a1=5\\b1=15\\a2=3\\b2=18\\a3=7\\b3=21\\a4=8[/tex]
we know that
[tex]\frac{b1}{a1}=\frac{15}{5}\\ \\b1=3*a1[/tex]
[tex]\frac{b2}{a2}=\frac{18}{6}\\ \\b2=3*a2[/tex]
[tex]\frac{b3}{a3}=\frac{21}{7}\\ \\b3=3*a3[/tex]
[tex]a4=8[/tex]
so
the next term should be
[tex]b4=3*a4=3*8=24[/tex]
therefore
the answer is
[tex]24[/tex]
