how do I work this out? in maths I always struggle the most with word problems I never know what operation to use or what to start with what could I use to improve and learn how to calculate worded maths problems like this one?
how do you actually know and understand what to do first
The question is asking you the cost of the electricity that she's used. So they give you the old and new reading. So if you assume that the old reading is from a month ago and the new reading is today, the difference between them is the total electricity used. Then they give you the cost per unit, so you multiply it by the units used.
So:
New reading - Old reading = units of electricity used
Units used x cost per unit = cost of the electricity used.