(9+d)*8=9*8+d*8 what property is this?

In general the distribute property is this

a*(b+c) = a*b + a*c

or

(b+c)*a = b*a + c*a

the basic idea is that we multiply the outer term 'a' with each term inside (those terms being b and c).

In your problem, the outer term is 8 and the inner terms are 9 and d

Another Example:

(2+3)*4 = 2*4+3*4 = 8+12 = 20

note how

(2+3)*4 = 5*4 = 20

b is the final answer! : )

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