Concept:Use the BODMAS rule: first solve Brackets, then Multiplication, then Addition and Subtraction from left to right.Explanation:Start with the bracket: 31+23=54. The expression becomes 91−56+78−54+45×2.Next, multiplication: 45×2=90. Now we have 91−56+78−54+90.Group positive numbers: 91+78+90=259. Group negative numbers: 56+54=110.Subtract: 259−110=149.Alternatively, solve stepwise: 91−56=35; 35+78=113; 113−54=59; 59+90=149.Check unit digit: 1−6+8−4+0=−1, so result ends in 9 (since 10−1=9). Only option 149 ends with 9.Answer:149 (Option A)