**Example** : $A$ is 10% bigger than $B$ means that $A = (1 + 0.10)B = 1.10B$. And: $A$ is 10% less than $B$ means $A = 1 - 0.10 = 0.90B$.
**Example** : If I have $200$ apples and you have $300$ apples, then $300/200 = 1.50 = 1 + 0.50$, so you have $50$% more apples that I do. So that is $300 = 200 + 0.50\cdot 200$.
Let $M$ be Mary's income, $T$ be Tim's income, and $J$ be Juan's income. Then you have $M = 1.6T$ and $T = 0.6J$, so $M = 1.6\cdot 0.6J = ...$
As a sidenote: the equations that you wrote down don't really make sense. The first one, for example, would imply that Tim's income is zero (subtract Mary on both sides).