So it tell us that he is able to get 5 hits out of 7 and to find how much he could make if 210 chances
\(\frac{5}{7} = \frac{x}{210}\)
We solve what can be solved
\(0.7 = \frac{x}{210}\)
Then we leave our variable alone
\(0.7 *210=x\)
Last we solve
\(x=147\)
In this case we can see that he could make 147 hits out of 210 bats.