write as a power of 4 4^5 x 4^7 and (4^5)^3

And using  (a^m)^n = a^(m * n),  we have

(4^5)^3  = 4^(5 * 3)  =  4 ^15

In general:

$$a^m\times a^n = a^{m+n}$$

and

$$(a^m)^n=a^{m\times n}$$

Can you do your question now?

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I know that bit but the answer said to a power of 4

that part confused me

The question is write as a power of 4.  So:

$$4^5\times 4^7 = 4^{5+7}=4^{12}$$

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