Respuesta :

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.
andy2020125
77=x+x-13
77=2x-13
-2x=-13-77
-2x=-90
x=45
Sydney's age is 45

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