Well if you have 60 and she has 120 i will set it out as a sequence week by week 60,67,74,81,88,95,102,109,116,123,130,137,144,151,158,165,172,179,186,193,200,207,214,221,228,235,242,249,256,263,270 120,125,130,135,140,145,150,155,160,165,170,175,180,185,190,195,200,205,210,215,220,225,230,235,240, 245,250,255,260,265,270 it would take 31 weeks and the total is 270
You have to start out with the distributive property 5 times 2 times c is 10+5c; now you have to subtract 5c on both sides in the upside down T chart, now its 10=45+c and your answer will be c=4.5.