Inequalities regarding CDF, expected value

Let F be the distribution function of a random variable $X$ such that $\mathbb E[X]=10$. It follows that

a) if $F(-10)=0$ then $P(X\geq 30)\leq 1/2$

b) if $F(-10)=0$ then $P(X\geq30)\leq 1/3$

c) if $Var(X)=1$ then $P(X\geq30)\leq 1/5$

For a),b),c) decide if sentence is true or false.