We will say the variable to be x. So we will say her sister is x years old. susan is x + 5 years old
susan = x+5 sister = x the equation wll be (x + 5) + x =51 ans = (x+5) + x = 51
if you want to continue yo first collect the like terms wich are the variables that look alike and simplify them
in this case you take x and add to x making it 2x then you cross 5 to the other side of the equal sign then because t is positive it will turn to negative. then you will minus it wiy=th 51
in equation form it is done like this; (x+5) + x = 51 x+x +5 = 51 2x + 5 = 51 → 2x = 51 - 5 2x = 46 2x/2 =46/2 x = 23
if her sister is 23 years old then susan is 23 + 5 years old
