According to the general equation of the line which is y= mx +c
where m is the slope and c is a constant
we notice here in the general equation that the slope is the coefficient of x when the coefficient of y = 1
so back to the Q.15
a) slope = 1/2
b) slope = 0
c) slope = 4
d) we need the equation to be in the general form and the coefficient of y=1, so we devide all the equation by 2
and it will be as follow y = -5/2 x + 99/2
so the slope = -5/2
Q.16:
multiply both sides by 6/5
x= 7/10