60% of the remainder was spent on the oven so 40% of the remainder was left.

That is equal to ¼ of the salary.


¼ of salary → 40% of remainder

Salary → 40% of remainder × 4
Salary → 160% of remainder


This is as good as saying :

Salary = 160 units
Remainder = 100 units

So, that $1200 spent on the TV
= 160 units - 100 units
= 60 units


1 unit = $1200 ÷ 60 = $20

Salary = 160 units

= 160 × $20
= $3200

Alternatively,

Rewrite 60% and 40% as fractions.


60% = 60/100 = 3/5
40% = 40/100 = 2/5


So we can let the money left at the end be 2 units.
The remainder is 5 units.
The amount spent on the oven is 3 units

2 units = ¼ of salary

Salary = 2 units × 4 = 8 units


Amount spent on TV = 8 units - 5 units
= 3 units


3 units = $1200
1 unit = $1200 ÷ 3 = $400

Salary = 8 units
= $400 × 8
= $3200