Ok so if they payed a flat fee it would just be 50 per month so 50x, then $8 per month would be 8m and $4 per month would be 4s. Here is the equation: 50x+8m+4s=T, then it's asking you for how much will you pay for 12 months so, you plug in 12 to all the variables: 50(12)+8(12)+4(12)=T then you simplify it by multiplying all of them and get 600+96+48=T, then you simplify it even more by adding the left side of the equation and you get $744=T so for 12 months it would be $744.
Hope this helps.