Let [tex] b [/tex] be the number of three points baskets, and [tex] t [/tex] be the number of three points tries. We are given
[tex] \dfrac{b}{t} = \dfrac{2}{7} \iff 2t=7b [/tex]
Also, we know that the team scored 30 points from three points baskest. Since these baskest are worth 3 points, we have
[tex] 3b=30 \iff b = 10 [/tex]
Now, we also know that [tex] 2t=7b [/tex]. If we plug the known value for b, we can solve for t:
[tex] 2t = 7\cdot 10 \iff 2t = 70 \iff t = 35 [/tex]