Note: If the mapping has equal interval (difference) for the y and x interval of 1 , you can use the general linear sequence formula to find the rule of the mapping. Un=U1+(n−1)d In the mapping, Un=y and n=x and U1, the first value of y U1=15 y=15+(x−1)d The d is the interval between each consecutive y In this mapping, d=30−15=45−30=60−45=15 We can substitute our d and simplify the expression for y y=15+(x−1)d y=15+(x−1)15 y=15+15×x−1×15 y=15+15x−15 y=15x+15−15 y=15x+0 y=15x x⟶15x