Explanation:
it is a simple scenario, where 2 values are added for a total.
and then we know the total and one of the 2 values. how big is the second value ?
that is why we use variables for an unknown value - in this case y.
this days nothing else but
y + 1.7 = 6.2
now we get y by simply subtracting 1.7 from both sides of the equation :
y + 1.7 - 1.7 = 6.2 - 1.7
y + 0 = 4.5
y = 4.5