Phil solved the equation x + 235.12 = 310.21, and found the solution to be 545.33. is he correct? if not, what was his mistake?

No.  He added 235.12 and 310.21, whereas he should have subtracted 235.12 from 310.21.

Step-by-step explanation:

First note that the "jump" from 235 (approx.) to 310 (approx) could not possibly  be 545 (approx.)  Looks like Phil added together 235 and 310, whereas he should have subtracted 235 from 310.  Doing so now yields 75 (approx).

For the purpose of answering this question, rounded off numbers are perfectly adequate.  If an "exact" answer is wanted, then subtract 235.12 from 310.21; the result should be 75.09 (which is only 0.09 off from my estimate).

a.

step-by-step explanation:

step 1 distribute 2 to every term in the parentheses

step 2 add 10 on both sides of the equal sign

there are 70 more legs than eyes at the dog show (196 – 126 = 70). dogs have two more legs than eyes, and humans have the same number of legs as eyes. thus 70 is twice the number of dogs at the show, so the number of dogs is half of 70, which is 35. to get the number of humans, subtract 35 from 63: 63 – 35 = 28.

step-by-step explanation: