Need help with problem 7, it is a real analysis and measure theory course

7. In this problem we use Lebesgue measure A on R. Let f and g be Borel measurable functions on R that belong to L' (R). It is a fact that the function that sends (x, y) to f(x - y)g(y) is measurable with respect to the product o-algebra BIR] & BIR]. (a) Show that SIf(x - y)g(y)| d)(y)