Devaughn is 13 years younger than sydney. the sum of their ages is77 what is sydney's age?

S is sydney's age. devaughn's age is d. d=s-13. The total sum is 77=s+d OR 77=s+s-13. 77=2s-13. add 13 to both sides. 90=2s. sydney's age is 45. to check, substitute sydney's age in. d=45-13=32. 77=45+32=77.

77=x+x-13
77=2x-13
-2x=-13-77
-2x=-90
x=45
Sydney's age is 45

The first option would be correct if it were one half and not one