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)dIn the mapping, Un=y and n=x and U1, the first value of yU1=15y=15+(x−1)dThe d is the interval between each consecutive yIn this mapping, d=30−15=45−30=60−45=15We can substitute our d and simplify the expression for yy=15+(x−1)dy=15+(x−1)15y=15+15×x−1×15y=15+15x−15y=15x+15−15y=15x+0y=15xx⟶15x