The function that has real zeros at x = 3 and 7 is f(x) = x² - 10x + 21
In order to determine the equation equation with real zero at x = 3 and x = 7
The equivalent factors will be (x - 3) and (x - 7)
Multiplying the factors
f(x) = (x - 3)(x - 7)
f(x) = x² - 7x - 3x + 21
f(x) = x² - 10x + 21
Hence the function that has real zeros at x = 3 and 7 is f(x) = x² - 10x + 21