So now what you want to do is turn 5/8 into a decimal and we do this by dividing the numerator by the denominator( In this case 5÷8=0.625) Now we multiply L×W(2.45×0.625=1.53125) This is the area if i am correct
Now another at to do it is doing this you do 2.45×5=12.25÷8=1.53125 which is the same answer.
Now for perimeter we do this L+W×2 so we do 2.45+0.625=3.075×2= 6.15 so this is your answer.
Now you said to estimate this and if you have to round your answer you do it by depending on what place value you round to you look at the one before and if the number in the digit is greater than 5 you add 1 to the value you round to but if it is less than 4 you don't do anything and just cover over everything else
