You are x in the solution
sister is y in the equation
x-2+y-2=57
x+y=61
2(x-7)+2=32
2x-14=30
2x=44
x=22 your age
y=39, your sister's age
2 years ago they were 20 and 37=57
7 years ago, sister was 32 and you were 15--32 is 2 x 15 +2.