Question 66048
2/3 (6R + S)  + 1/4 (8R + 15S)
Your LCD is 3*4=12, whatever you do to get the denominator = to 12, do to the numerator:
{{{((4*2)/(4*3))(6R+S)+((3*1)/(3*4))(8R+15S))}}}
{{{(8/12)(6R+S)+(3/12)(8R+15S)}}}
{{{48R/12+8S/12+24R/12+45S/12}}}
{{{(48R+8S+24R+45S)/12}}}
{{{((48+24)R+(8+45)S)/12}}}
{{{highlight((72R+53S)/12)}}}
Happy Calculating!!!!