Question 453167
If your ages now are 57 and 4 than in x years you(G) and your granddaughter(D) will be:
:
G = 57+x 
D = 4+x
:
At the same time, after x years, you should be 3 times older :
:
G=3D
:
57+x=3(4+x), this is equation you're looking for.