You need to find the least common denominator first which is 4. 3 3/4 can stay the same but you must have like denominators to add so change 1 1/2 to 1 2/4 by multiplying by 2/2. You know have like denominators and you can add whole numbers first 3+1=4 and then the fractions 3/4+2/4= 5/4 which is also 1 1/4. Now you add 4 so your answer is 5 1/4