a rectangular piece of plastic sheet measures 1 m by 70 cm. find its cost at the rate rupees 80 per square metre.

1m = 100 cm
70cm = 70/100 = 0.7 m
area of rectangular piece of plastic sheet = l x b
                                                                  1m x 0.7m
                                                                   0.7m².
cost at the rate rs. 80 per sq. m = 0.7 x 80 = rs. 56.0
                                                                     rs. 56.
hope this help you .... :))