Question 857354
let C = Cornelius, P = Plato, let n = number of years
C + n15 > P - n12
957 + n15 > 1200 - n12
27n > 243
n > 9
say n is 10
957 + 150 > 1200 - 120
1107 > 1080
our answer of 10 years checks  :-)