Vector Fields / Flow Lines

Ok, I am unable to figure out the following problem.

**Problem:**

The following equation is used in the definition of a flow line: **x'**(t) = **F**(**x**(t))

Calculate the flow line **x**(t) of the given vector field **F **that passes through the indicated point at the specified value of t.

**F**(x,y) = -x**i **+ y**j**; **x**(0) = (2,1)

The way I began this problem is to have **x**(t) = (x(t), y(t)) and then **x'**(t) = (x'(t), y'(t)). Then I don't know how to proceed. I tried equating components like so:

x'(t) = -x

y'(t) = y

But...that doesn't appear to work. Thanks for any help. I know my method is wrong because the next problem is similar, but I am not getting the same answer.