A two digit number has a tens digit and a ones digit.
Let's say x = tens digit and y = ones digit
"The sum of the digits is 5"
x + y = 5
The next phrase is "the number multiplied by 3 is 42" but we need to represent the number using the digits. So they need to be multiplied first by their place value and added together. [Example: 34 = 3(10) + 4(1)]
The number is: 10x + y
3(10x + y) = 42
The system of equations: (two equations for two unknowns)
x + y = 5
30x + 3y = 42
Then you can use substitution or elimination to combine and solve.
I'll use elimination, multiply the entire top equation by -3 and add the equations together. y will cancel out
-3x - 3y = -15
30x + 3y = 42
------------------
27x + 0 = 27
x = 1
then plug x = 1 into either equation to find y
1 + y = 5
y = 4
remember the x and y represent digits so the number xy is 14
