Every number consists of digits which have their own value. If the number consists of 3 digits, then the rightmost digit is for ones, middle digit is for tens and leftmost digit is for hundreds (it goes on and on with more-than-3-digit-numbers). About your task:
Hundred digit is smaller than tens digit and tens digit is smaller than ones digit. It means that the leftmost digit is the lowest, the rightmost digit is the greatest and the middle digit is a value between both of them.
For example:
123, 258, 346, 789, 278, 568 etc. etc.
Let F be the father's current age, and E be Evie's current age.
F = E + 36 this is the current relation between the ages
F + 3 = 5(E + 3) this the relationship in 3 year (hence the + 3)
Then solve by substituting one equation into another:
(E + 36) + 3 = 5(E + 3)
E + 39 = 5E + 15
24 = 4E
6 = E
Evie's current age is 6.
One vertex the rectangle lies on the straight line x + y = 6, which means that the sum of lengths of two adjacent sides is 6. Then the perimeter is 12 cm.
The answer is D :)))))))))
