I know how to do 67 I keep getting the answer wrong for 68 I

I know how to do #67. I keep getting the answer wrong for #68. I put 20/6 = 4 + x/x and got x = 1.7 but the answer is supposed to be 5.7.

B 67. If CD 7, DA 3, and DE 10, then AB 68, If AB 20, DE 6, and AD 4, then AC

Let CD = x

Then, AC= 4 +x

Now, CD / AD = DE /AB

x /4 = 6 /20

Cross multiply both sides, we get

20x = 24

x = 24/20 = 12/10 = 1.2

There fore, AC = 4 + 1.2 = 5.2