Of course, it's always helpful to be fluent in your single-digit multiplication, to know that 7 x 8 = 56.
But if you're not there yet, you can also know that multiplying by 8 is the same as multiplying by 4, then doubling. That's because a number X 8 = number X 4 X 2.
So 7 X 8 = (7 X 4) X 2 = 28 X 2 = 56