Form a linear equation in two variables for each of the following :
a) Pak Osman bought x oranges and y apples with a total amount of RM50. He sold an orange and an apple for RM0.60 and RM0.70 respectively. After he sold all the fruits, he earned a profit of RM10.
b) The sum of numbers x and y is five times the difference between the two numbers. The value of x is greater than the value of y.