Why isn’t my function evaluating to an explicit number?

I’m just wondering why my function is not evaluating as I think it should. I put in the following:

dp = {{0, 71}, {1, 71}, {2, 71}, {3, 70}, {4, 69}, {5, 67}, {6,65}, {7, 63}, {8, 61}, {9, 60}, {10, 60}, {11, 61}, {12, 63}, {13,65}, {14, 66}, {15, 67}, {16, 67}, {16, 67}, {17, 66}, {18,65}, {19, 63}, {20, 60}, {21, 58}, {22, 56}, {23, 55}}; f = Fit[dp, {1, x, x^2, x^3, x^4, x^5, x^6, x^7}, x]; f[3] 

but as output I get

(71.121 - 1.29633 x + 1.34837 x^2 - 0.504693 x^3 + 0.0700859 x^4 - 0.00447611 x^5 + 0.000134178 x^6 - 1.53469*10^-6 x^7)[3] 

The output I want is the polynomial’s value at x=3.