Every rectangle area question is the same two moves: find the two side lengths, then multiply them. That's it.
The Two Moves
One — read off the width and the height. They're the two side lengths. It doesn't matter which you call which.
Two — multiply. Area = width × height. Write it, drop the numbers in, multiply.
A Worked One
A rectangle 9 long and 4 wide: 9 × 4 = 36, so the area is 36 square units. If those were metres, that's 36 m².
Handy shortcut: with a tricky number, break it up. Area of 12 × 5? Do 10 × 5 = 50 and 2 × 5 = 10, then add: 60. Same answer, friendlier sums.
Decimals Are No Different
If a side is 2.5 m, the method doesn't change: 2.5 × 4 = 10 m². Just multiply carefully and keep the "square" on the units.