A study compares three population means. Three independent samples with 15 observations are each taken. The SSE = 1246 and the SST = 1600. What is the value of the F statistic?

I have no idea how to do this problem. I do know the answer is 5.97 I just have no idea how to get that as an answer... Help me please! Thank you.

First, we know that the total sum of squares, SST, is the sum of the regression sum of squares (SSR) and the error sum of squares (SSE). So

SST = SSE + SSR

and

SSR = SST - SSE = 1600 -1246 = 354

We can calculate the number of degrees of freedom in SSR and SST as

df(SSR) = g - 1 = 3 - 1 = 2
df(SSE) = N - g = 45 - 3 = 42

where g is the number of coefficients in the regression equation and N is the total number of samples.

Now the formula for calculating F is

F = \frac{SSR * df(SSE)}{SSE*df(SSR)}=\frac{354 * 42}{1246*2}=5.96629

See this page for more details:
Correlation between factors (http://home.comcast.net/~sharov/PopEcol/lec4/corfact.html)

Where did that 45 come from ?