Can someone explain the following problem?

.5(g+10)=50

Well, first you need to distribute the .5 to everything in the parenthesis. so you would come out with:
.5g + 5 = 50
now, you want to isolate the variable. so subtract 5 from both sides. You're left with
.5g = 45
now, divide 45 by .5
you're left with g = 90!

0 is the answer. 0+10 is 10, 10*5 is 50, 50=50.

B. because the 7 represents "seven times", x represents "a number", 12 represents "plus twelve", and -4 represents "minus four"