Answer:
b=8.5cm
Explanation:
tanx (this represents tan theta, it's just easier to type) is equal to 0.6 and since the tanx ratio is opp/adj, we know that opp/adj = 0.6
To find what b is (adjacent as it is adjacent to the angle being used and it is not the hypotenuse), we just have to rearrange.
0.6=5.1/adj
to solve for adj, we can switch 0.6 and adj. (This works because to get adj by itself on one side you would multiply it to the other side and then divide 0.6 from both sides --> simple algebra)
so then you have
adj=5.1/0.6
adj=8.5cm
(if you want to check your solution you can use pythagoeran theorem, a^2+b^2=c^2) and sub everything in and make sure all the numbers equal the right thing!