Basically you need to find the full value of x, so you multiply it by 2 1/2x * 2 = x and because this is algebra, what you do to one side you have to do to the other, so -11 x 2 = -22.
15r means that she burns 15 calories per min, for as many mins as she ran. EG: if she ran for 10 min, then she burned 150 cals. The other one I'm not so sure.