To know the answer, you must 'sum up' or 'add' the two amounts. So you will have (5 + 10 = 15) dollars now. One way of visualizing addition of numbers is by looking at the number line as a series of steps in a staircase. Each step in the staircase is labeled with numbers starting from 1, 2, 3, 4, ... up to the maximum number possible, in ascending order. When you add, you ascend steps and when you subtract, you descend steps downwards.