Ok so first with a you have a=2 b=5 c=7 and the problems are 2a+10 and 2b+c Well to do this we are going to right 2a+10 as 2*a+10 So now lets replace a. and since a=2 we have 2*2+10 2*2=4+10=14 So A is 14 and now for be we have 2b+c Lets re-write it as 2*b+c and now replace 2*5+7 2*5=10+7=17 b is 17. Now with the next (4) For a it is x=7 Subtract 3x from both sides. Subtract 5 from both sides. x=7 and for B x=3 Subtract 3x from both sides. Add 10 to both sides. Divide both sides by 4. x=3 Hope this helps!
